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 $146.70   12.307%   $164.7544   $164.75   $164.75   $164.80  
  Purchase #2 $50.46   9.592%   $55.3001   $55.30   $55.30   $55.30  
  Purchase #3 $224.63   3.546%   $232.5954   $232.60   $232.60   $232.60  
  Purchase #4 $130.41   11.847%   $145.8597   $145.86   $145.85   $145.90  
  Purchase #5 $63.51   5.382%   $66.9281   $66.93   $66.95   $66.90  
  Purchase #6 $130.47   11.147%   $145.0135   $145.01   $145.00   $145.00  
  Purchase #7 $232.32   5.120%   $244.2148   $244.21   $244.20   $244.20  
  7 purchase totals = $978.50       $1,054.6660   $1,054.66   $1,054.65   $1,054.70