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 $206.81   10.415%   $228.3493   $228.35   $228.35   $228.30  
  Purchase #2 $181.80   11.871%   $203.3815   $203.38   $203.40   $203.40  
  Purchase #3 $178.99   11.474%   $199.5273   $199.53   $199.55   $199.50  
  Purchase #4 $141.81   12.310%   $159.2668   $159.27   $159.25   $159.30  
  Purchase #5 $48.77   5.857%   $51.6265   $51.63   $51.65   $51.60  
  Purchase #6 $221.73   3.104%   $228.6125   $228.61   $228.60   $228.60  
  Purchase #7 $194.47   5.220%   $204.6213   $204.62   $204.60   $204.60  
  7 purchase totals = $1,174.38       $1,275.3852   $1,275.39   $1,275.40   $1,275.30