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 $208.78   11.207%   $232.178   $232.18   $232.20   $232.20  
  Purchase #2 $106.98   5.524%   $112.8896   $112.89   $112.90   $112.90  
  Purchase #3 $161.33   4.850%   $169.1545   $169.15   $169.15   $169.20  
  Purchase #4 $241.99   3.135%   $249.5764   $249.58   $249.60   $249.60  
  Purchase #5 $146.57   6.545%   $156.163   $156.16   $156.15   $156.20  
  Purchase #6 $113.34   6.271%   $120.4476   $120.45   $120.45   $120.40  
  Purchase #7 $224.57   9.283%   $245.4168   $245.42   $245.40   $245.40  
  7 purchase totals = $1,203.56       $1,285.8259   $1,285.83   $1,285.85   $1,285.90