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 $62.37   10.490%   $68.9126   $68.91   $68.90   $68.90  
  Purchase #2 $65.38   4.848%   $68.5496   $68.55   $68.55   $68.50  
  Purchase #3 $152.45   8.216%   $164.9753   $164.98   $165.00   $165.00  
  Purchase #4 $235.78   12.374%   $264.9554   $264.96   $264.95   $265.00  
  Purchase #5 $170.41   4.834%   $178.6476   $178.65   $178.65   $178.60  
  Purchase #6 $205.84   9.130%   $224.6332   $224.63   $224.65   $224.60  
  Purchase #7 $115.44   12.687%   $130.0859   $130.09   $130.10   $130.10  
  7 purchase totals = $1,007.67       $1,100.7596   $1,100.77   $1,100.80   $1,100.70