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 $211.69   12.433%   $238.0094   $238.01   $238.00   $238.00  
  Purchase #2 $80.83   3.160%   $83.3842   $83.38   $83.40   $83.40  
  Purchase #3 $13.72   6.419%   $14.6007   $14.60   $14.60   $14.60  
  Purchase #4 $66.97   13.693%   $76.1402   $76.14   $76.15   $76.10  
  Purchase #5 $232.96   12.582%   $262.271   $262.27   $262.25   $262.30  
  Purchase #6 $93.41   13.860%   $106.3566   $106.36   $106.35   $106.40  
  Purchase #7 $202.84   11.687%   $226.5459   $226.55   $226.55   $226.50  
  7 purchase totals = $902.42       $1,007.3080   $1,007.31   $1,007.30   $1,007.30