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 $53.38   10.438%   $58.9518   $58.95   $58.95   $59.00  
  Purchase #2 $232.50   7.874%   $250.8071   $250.81   $250.80   $250.80  
  Purchase #3 $180.43   9.288%   $197.1883   $197.19   $197.20   $197.20  
  Purchase #4 $124.53   9.786%   $136.7165   $136.72   $136.70   $136.70  
  Purchase #5 $49.99   9.540%   $54.759   $54.76   $54.75   $54.80  
  Purchase #6 $36.89   10.670%   $40.8262   $40.83   $40.85   $40.80  
  Purchase #7 $70.52   6.417%   $75.0453   $75.05   $75.05   $75.00  
  7 purchase totals = $748.24       $814.2942   $814.31   $814.30   $814.30