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 $175.92   11.152%   $195.5386   $195.54   $195.55   $195.50  
  Purchase #2 $234.38   5.388%   $247.0084   $247.01   $247.00   $247.00  
  Purchase #3 $195.50   5.361%   $205.9808   $205.98   $206.00   $206.00  
  Purchase #4 $25.29   12.431%   $28.4338   $28.43   $28.45   $28.40  
  Purchase #5 $242.70   8.378%   $263.0334   $263.03   $263.05   $263.00  
  Purchase #6 $70.87   8.388%   $76.8146   $76.81   $76.80   $76.80  
  Purchase #7 $37.60   9.140%   $41.0366   $41.04   $41.05   $41.00  
  7 purchase totals = $982.26       $1,057.8462   $1,057.84   $1,057.90   $1,057.70