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 $57.32   11.122%   $63.6951   $63.70   $63.70   $63.70  
  Purchase #2 $62.28   12.126%   $69.8321   $69.83   $69.85   $69.80  
  Purchase #3 $5.74   4.428%   $5.9942   $5.99   $6.00   $6.00  
  Purchase #4 $45.68   7.284%   $49.0073   $49.01   $49.00   $49.00  
  Purchase #5 $63.39   13.109%   $71.6998   $71.70   $71.70   $71.70  
  Purchase #6 $82.63   13.385%   $93.69   $93.69   $93.70   $93.70  
  Purchase #7 $71.52   9.793%   $78.524   $78.52   $78.50   $78.50  
  7 purchase totals = $388.56       $432.4425   $432.44   $432.45   $432.40