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 $181.93   11.152%   $202.2188   $202.22   $202.20   $202.20  
  Purchase #2 $59.55   10.874%   $66.0255   $66.03   $66.05   $66.00  
  Purchase #3 $123.96   8.645%   $134.6763   $134.68   $134.70   $134.70  
  Purchase #4 $134.29   5.236%   $141.3214   $141.32   $141.30   $141.30  
  Purchase #5 $43.82   4.129%   $45.6293   $45.63   $45.65   $45.60  
  Purchase #6 $193.98   8.420%   $210.3131   $210.31   $210.30   $210.30  
  Purchase #7 $160.81   4.619%   $168.2378   $168.24   $168.25   $168.20  
  7 purchase totals = $898.34       $968.4222   $968.43   $968.45   $968.30