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 $90.97   6.273%   $96.6765   $96.68   $96.70   $96.70  
  Purchase #2 $53.52   8.757%   $58.2067   $58.21   $58.20   $58.20  
  Purchase #3 $69.35   3.374%   $71.6899   $71.69   $71.70   $71.70  
  Purchase #4 $227.46   13.504%   $258.1762   $258.18   $258.20   $258.20  
  Purchase #5 $60.40   9.442%   $66.103   $66.10   $66.10   $66.10  
  Purchase #6 $173.57   9.208%   $189.5523   $189.55   $189.55   $189.60  
  Purchase #7 $161.48   4.809%   $169.2456   $169.25   $169.25   $169.20  
  7 purchase totals = $836.75       $909.6502   $909.66   $909.70   $909.70