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 $60.62   11.597%   $67.6501   $67.65   $67.65   $67.70  
  Purchase #2 $165.62   8.361%   $179.4675   $179.47   $179.45   $179.50  
  Purchase #3 $55.67   8.152%   $60.2082   $60.21   $60.20   $60.20  
  Purchase #4 $209.88   12.327%   $235.7519   $235.75   $235.75   $235.80  
  Purchase #5 $180.80   9.276%   $197.571   $197.57   $197.55   $197.60  
  Purchase #6 $195.88   8.454%   $212.4397   $212.44   $212.45   $212.40  
  Purchase #7 $31.55   4.305%   $32.9082   $32.91   $32.90   $32.90  
  7 purchase totals = $900.02       $985.9966   $986.00   $985.95   $986.10