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 $86.79   10.240%   $95.6773   $95.68   $95.70   $95.70  
  Purchase #2 $15.49   9.185%   $16.9128   $16.91   $16.90   $16.90  
  Purchase #3 $54.39   3.164%   $56.1109   $56.11   $56.10   $56.10  
  Purchase #4 $13.99   11.381%   $15.5822   $15.58   $15.60   $15.60  
  Purchase #5 $178.55   13.813%   $203.2131   $203.21   $203.20   $203.20  
  Purchase #6 $166.73   8.120%   $180.2685   $180.27   $180.25   $180.30  
  Purchase #7 $181.46   11.322%   $202.0049   $202.00   $202.00   $202.00  
  7 purchase totals = $697.40       $769.7697   $769.76   $769.75   $769.80