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 $42.89   5.595%   $45.2897   $45.29   $45.30   $45.30  
  Purchase #2 $168.60   9.492%   $184.6035   $184.60   $184.60   $184.60  
  Purchase #3 $201.46   6.586%   $214.7282   $214.73   $214.75   $214.70  
  Purchase #4 $83.92   11.526%   $93.5926   $93.59   $93.60   $93.60  
  Purchase #5 $19.51   9.519%   $21.3672   $21.37   $21.35   $21.40  
  Purchase #6 $186.92   5.738%   $197.6455   $197.65   $197.65   $197.60  
  Purchase #7 $242.41   5.511%   $255.7692   $255.77   $255.75   $255.80  
  7 purchase totals = $945.71       $1,012.9959   $1,013.00   $1,013.00   $1,013.00