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 $246.59   11.699%   $275.4386   $275.44   $275.45   $275.40  
  Purchase #2 $217.94   7.232%   $233.7014   $233.70   $233.70   $233.70  
  Purchase #3 $26.70   8.376%   $28.9364   $28.94   $28.95   $28.90  
  Purchase #4 $207.66   4.277%   $216.5416   $216.54   $216.55   $216.50  
  Purchase #5 $246.82   3.510%   $255.4834   $255.48   $255.50   $255.50  
  Purchase #6 $191.77   6.619%   $204.4633   $204.46   $204.45   $204.50  
  Purchase #7 $77.89   12.666%   $87.7555   $87.76   $87.75   $87.80  
  7 purchase totals = $1,215.37       $1,302.3202   $1,302.32   $1,302.35   $1,302.30