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 $51.91   5.536%   $54.7837   $54.78   $54.80   $54.80  
  Purchase #2 $224.85   5.193%   $236.5265   $236.53   $236.55   $236.50  
  Purchase #3 $130.30   8.209%   $140.9963   $141.00   $141.00   $141.00  
  Purchase #4 $161.68   5.146%   $170.0001   $170.00   $170.00   $170.00  
  Purchase #5 $220.75   5.442%   $232.7632   $232.76   $232.75   $232.80  
  Purchase #6 $63.76   6.616%   $67.9784   $67.98   $68.00   $68.00  
  Purchase #7 $162.94   11.129%   $181.0736   $181.07   $181.05   $181.10  
  7 purchase totals = $1,016.19       $1,084.1218   $1,084.12   $1,084.15   $1,084.20