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 $59.40   4.393%   $62.0094   $62.01   $62.00   $62.00  
  Purchase #2 $126.70   13.363%   $143.6309   $143.63   $143.65   $143.60  
  Purchase #3 $143.92   6.319%   $153.0143   $153.01   $153.00   $153.00  
  Purchase #4 $77.49   3.730%   $80.3804   $80.38   $80.40   $80.40  
  Purchase #5 $214.58   9.220%   $234.3643   $234.36   $234.35   $234.40  
  Purchase #6 $77.49   7.474%   $83.2816   $83.28   $83.30   $83.30  
  Purchase #7 $39.98   13.204%   $45.259   $45.26   $45.25   $45.30  
  7 purchase totals = $739.56       $801.9399   $801.93   $801.95   $802.00