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 $30.87   13.282%   $34.9702   $34.97   $34.95   $35.00  
  Purchase #2 $53.58   10.308%   $59.103   $59.10   $59.10   $59.10  
  Purchase #3 $186.83   3.429%   $193.2364   $193.24   $193.25   $193.20  
  Purchase #4 $63.75   5.667%   $67.3627   $67.36   $67.35   $67.40  
  Purchase #5 $228.60   12.654%   $257.527   $257.53   $257.55   $257.50  
  Purchase #6 $120.53   12.399%   $135.4745   $135.47   $135.45   $135.50  
  Purchase #7 $72.52   7.523%   $77.9757   $77.98   $78.00   $78.00  
  7 purchase totals = $756.68       $825.6495   $825.65   $825.65   $825.70