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 $180.82   12.405%   $203.2507   $203.25   $203.25   $203.30  
  Purchase #2 $153.79   9.319%   $168.1217   $168.12   $168.10   $168.10  
  Purchase #3 $36.66   13.870%   $41.7447   $41.74   $41.75   $41.70  
  Purchase #4 $182.77   8.146%   $197.6584   $197.66   $197.65   $197.70  
  Purchase #5 $245.71   13.837%   $279.7089   $279.71   $279.70   $279.70  
  Purchase #6 $192.62   11.235%   $214.2609   $214.26   $214.25   $214.30  
  Purchase #7 $60.38   5.216%   $63.5294   $63.53   $63.55   $63.50  
  7 purchase totals = $1,052.75       $1,168.2747   $1,168.27   $1,168.25   $1,168.30