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 $56.89   13.320%   $64.4677   $64.47   $64.45   $64.50  
  Purchase #2 $216.69   11.388%   $241.3667   $241.37   $241.35   $241.40  
  Purchase #3 $101.58   5.495%   $107.1618   $107.16   $107.15   $107.20  
  Purchase #4 $171.28   5.122%   $180.053   $180.05   $180.05   $180.10  
  Purchase #5 $152.90   9.656%   $167.664   $167.66   $167.65   $167.70  
  Purchase #6 $42.26   4.354%   $44.1   $44.10   $44.10   $44.10  
  Purchase #7 $117.37   3.235%   $121.1669   $121.17   $121.15   $121.20  
  7 purchase totals = $858.97       $925.9801   $925.98   $925.90   $926.20