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 $74.45   11.481%   $82.9976   $83.00   $83.00   $83.00  
  Purchase #2 $167.27   8.164%   $180.9259   $180.93   $180.95   $180.90  
  Purchase #3 $247.82   8.674%   $269.3159   $269.32   $269.30   $269.30  
  Purchase #4 $5.64   10.858%   $6.2524   $6.25   $6.25   $6.30  
  Purchase #5 $175.64   10.438%   $193.9733   $193.97   $193.95   $194.00  
  Purchase #6 $234.32   12.161%   $262.8157   $262.82   $262.80   $262.80  
  Purchase #7 $178.86   10.297%   $197.2772   $197.28   $197.30   $197.30  
  7 purchase totals = $1,084.00       $1,193.5580   $1,193.57   $1,193.55   $1,193.60