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 $196.47   9.576%   $215.284   $215.28   $215.30   $215.30  
  Purchase #2 $62.27   3.777%   $64.6219   $64.62   $64.60   $64.60  
  Purchase #3 $78.57   3.751%   $81.5172   $81.52   $81.50   $81.50  
  Purchase #4 $141.69   13.598%   $160.957   $160.96   $160.95   $161.00  
  Purchase #5 $45.87   9.666%   $50.3038   $50.30   $50.30   $50.30  
  Purchase #6 $121.44   9.166%   $132.5712   $132.57   $132.55   $132.60  
  Purchase #7 $39.90   11.554%   $44.51   $44.51   $44.50   $44.50  
  7 purchase totals = $686.21       $749.7651   $749.76   $749.70   $749.80