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 $173.74   4.728%   $181.9544   $181.95   $181.95   $182.00  
  Purchase #2 $16.29   11.450%   $18.1552   $18.16   $18.15   $18.20  
  Purchase #3 $49.48   12.513%   $55.6714   $55.67   $55.65   $55.70  
  Purchase #4 $228.53   13.129%   $258.5337   $258.53   $258.55   $258.50  
  Purchase #5 $62.46   8.692%   $67.889   $67.89   $67.90   $67.90  
  Purchase #6 $111.82   3.122%   $115.311   $115.31   $115.30   $115.30  
  Purchase #7 $20.61   4.292%   $21.4946   $21.49   $21.50   $21.50  
  7 purchase totals = $662.93       $719.0093   $719.00   $719.00   $719.10