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 $58.91   6.767%   $62.8964   $62.90   $62.90   $62.90  
  Purchase #2 $173.29   9.436%   $189.6416   $189.64   $189.65   $189.60  
  Purchase #3 $104.44   6.608%   $111.3414   $111.34   $111.35   $111.30  
  Purchase #4 $149.54   5.241%   $157.3774   $157.38   $157.40   $157.40  
  Purchase #5 $95.63   11.188%   $106.3291   $106.33   $106.35   $106.30  
  Purchase #6 $250.84   13.604%   $284.9643   $284.96   $284.95   $285.00  
  Purchase #7 $85.73   10.782%   $94.9734   $94.97   $94.95   $95.00  
  7 purchase totals = $918.38       $1,007.5236   $1,007.52   $1,007.55   $1,007.50