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 $204.55   13.614%   $232.3974   $232.40   $232.40   $232.40  
  Purchase #2 $167.55   9.735%   $183.861   $183.86   $183.85   $183.90  
  Purchase #3 $99.34   5.620%   $104.9229   $104.92   $104.90   $104.90  
  Purchase #4 $199.48   5.717%   $210.8843   $210.88   $210.90   $210.90  
  Purchase #5 $113.40   6.272%   $120.5124   $120.51   $120.50   $120.50  
  Purchase #6 $53.81   8.403%   $58.3317   $58.33   $58.35   $58.30  
  Purchase #7 $222.67   8.380%   $241.3297   $241.33   $241.35   $241.30  
  7 purchase totals = $1,060.80       $1,152.2394   $1,152.23   $1,152.25   $1,152.20