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 $212.49   4.825%   $222.7426   $222.74   $222.75   $222.70  
  Purchase #2 $125.34   7.416%   $134.6352   $134.64   $134.65   $134.60  
  Purchase #3 $198.67   11.689%   $221.8925   $221.89   $221.90   $221.90  
  Purchase #4 $63.60   10.425%   $70.2303   $70.23   $70.25   $70.20  
  Purchase #5 $126.64   6.819%   $135.2756   $135.28   $135.30   $135.30  
  Purchase #6 $57.61   8.608%   $62.5691   $62.57   $62.55   $62.60  
  Purchase #7 $87.91   6.819%   $93.9046   $93.90   $93.90   $93.90  
  7 purchase totals = $872.26       $941.2499   $941.25   $941.30   $941.20