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 $227.33   11.629%   $253.7662   $253.77   $253.75   $253.80  
  Purchase #2 $245.73   6.751%   $262.3192   $262.32   $262.30   $262.30  
  Purchase #3 $186.89   9.461%   $204.5717   $204.57   $204.55   $204.60  
  Purchase #4 $178.45   5.375%   $188.0417   $188.04   $188.05   $188.00  
  Purchase #5 $176.80   6.289%   $187.919   $187.92   $187.90   $187.90  
  Purchase #6 $190.50   8.616%   $206.9135   $206.91   $206.90   $206.90  
  Purchase #7 $85.28   9.263%   $93.1795   $93.18   $93.20   $93.20  
  7 purchase totals = $1,290.98       $1,396.7108   $1,396.71   $1,396.65   $1,396.70