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 $69.52   6.453%   $74.0061   $74.01   $74.00   $74.00  
  Purchase #2 $59.59   3.361%   $61.5928   $61.59   $61.60   $61.60  
  Purchase #3 $95.35   12.815%   $107.5691   $107.57   $107.55   $107.60  
  Purchase #4 $146.85   13.166%   $166.1843   $166.18   $166.20   $166.20  
  Purchase #5 $187.33   7.200%   $200.8178   $200.82   $200.80   $200.80  
  Purchase #6 $70.97   11.249%   $78.9534   $78.95   $78.95   $79.00  
  Purchase #7 $222.43   6.742%   $237.4262   $237.43   $237.45   $237.40  
  7 purchase totals = $852.04       $926.5497   $926.55   $926.55   $926.60