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 $201.53   12.460%   $226.6406   $226.64   $226.65   $226.60  
  Purchase #2 $62.55   9.271%   $68.349   $68.35   $68.35   $68.30  
  Purchase #3 $121.73   11.202%   $135.3662   $135.37   $135.35   $135.40  
  Purchase #4 $217.55   12.638%   $245.044   $245.04   $245.05   $245.00  
  Purchase #5 $226.77   10.399%   $250.3518   $250.35   $250.35   $250.40  
  Purchase #6 $85.42   6.598%   $91.056   $91.06   $91.05   $91.10  
  Purchase #7 $80.73   10.669%   $89.3431   $89.34   $89.35   $89.30  
  7 purchase totals = $996.28       $1,106.1507   $1,106.15   $1,106.15   $1,106.10