Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $183.82   13.614%   $208.8453   $208.85   $208.85   $208.80  
  Purchase #2 $111.86   12.238%   $125.5494   $125.55   $125.55   $125.50  
  Purchase #3 $245.54   9.784%   $269.5636   $269.56   $269.55   $269.60  
  Purchase #4 $122.31   10.782%   $135.4975   $135.50   $135.50   $135.50  
  Purchase #5 $181.98   10.399%   $200.9041   $200.90   $200.90   $200.90  
  Purchase #6 $168.74   6.484%   $179.6811   $179.68   $179.70   $179.70  
  Purchase #7 $166.59   11.751%   $186.166   $186.17   $186.15   $186.20  
  7 purchase totals = $1,180.84       $1,306.2070   $1,306.21   $1,306.20   $1,306.20