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 $89.58   6.674%   $95.5586   $95.56   $95.55   $95.60  
  Purchase #2 $210.56   7.485%   $226.3204   $226.32   $226.30   $226.30  
  Purchase #3 $17.66   9.827%   $19.3954   $19.40   $19.40   $19.40  
  Purchase #4 $136.29   11.709%   $152.2482   $152.25   $152.25   $152.20  
  Purchase #5 $10.50   5.311%   $11.0577   $11.06   $11.05   $11.10  
  Purchase #6 $226.51   12.595%   $255.0389   $255.04   $255.05   $255.00  
  Purchase #7 $249.86   13.523%   $283.6486   $283.65   $283.65   $283.60  
  7 purchase totals = $940.96       $1,043.2678   $1,043.28   $1,043.25   $1,043.20