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 $57.98   6.437%   $61.7122   $61.71   $61.70   $61.70  
  Purchase #2 $67.52   3.302%   $69.7495   $69.75   $69.75   $69.70  
  Purchase #3 $84.78   9.830%   $93.1139   $93.11   $93.10   $93.10  
  Purchase #4 $79.52   4.126%   $82.801   $82.80   $82.80   $82.80  
  Purchase #5 $22.69   3.190%   $23.4138   $23.41   $23.40   $23.40  
  Purchase #6 $184.36   4.203%   $192.1087   $192.11   $192.10   $192.10  
  Purchase #7 $199.37   5.819%   $210.9713   $210.97   $210.95   $211.00  
  7 purchase totals = $696.22       $733.8704   $733.86   $733.80   $733.80