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 $69.61   6.250%   $73.9606   $73.96   $73.95   $74.00  
  Purchase #2 $140.36   13.661%   $159.5346   $159.53   $159.55   $159.50  
  Purchase #3 $20.90   4.537%   $21.8482   $21.85   $21.85   $21.80  
  Purchase #4 $25.60   7.505%   $27.5213   $27.52   $27.50   $27.50  
  Purchase #5 $220.89   7.597%   $237.671   $237.67   $237.65   $237.70  
  Purchase #6 $123.90   13.873%   $141.0886   $141.09   $141.10   $141.10  
  Purchase #7 $129.63   11.425%   $144.4402   $144.44   $144.45   $144.40  
  7 purchase totals = $730.89       $806.0645   $806.06   $806.05   $806.00