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 $51.68   12.387%   $58.0816   $58.08   $58.10   $58.10  
  Purchase #2 $164.96   8.295%   $178.6434   $178.64   $178.65   $178.60  
  Purchase #3 $234.91   5.289%   $247.3344   $247.33   $247.35   $247.30  
  Purchase #4 $167.79   9.445%   $183.6378   $183.64   $183.65   $183.60  
  Purchase #5 $119.90   6.599%   $127.8122   $127.81   $127.80   $127.80  
  Purchase #6 $205.65   9.405%   $224.9914   $224.99   $225.00   $225.00  
  Purchase #7 $56.53   10.305%   $62.3554   $62.36   $62.35   $62.40  
  7 purchase totals = $1,001.42       $1,082.8562   $1,082.85   $1,082.90   $1,082.80