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 $111.81   5.656%   $118.134   $118.13   $118.15   $118.10  
  Purchase #2 $93.60   4.230%   $97.5593   $97.56   $97.55   $97.60  
  Purchase #3 $119.34   12.416%   $134.1573   $134.16   $134.15   $134.20  
  Purchase #4 $146.28   10.157%   $161.1377   $161.14   $161.15   $161.10  
  Purchase #5 $123.70   7.484%   $132.9577   $132.96   $132.95   $133.00  
  Purchase #6 $231.27   12.343%   $259.8157   $259.82   $259.80   $259.80  
  Purchase #7 $218.56   7.227%   $234.3553   $234.36   $234.35   $234.40  
  7 purchase totals = $1,044.56       $1,138.1170   $1,138.13   $1,138.10   $1,138.20