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 $245.71   12.853%   $277.2911   $277.29   $277.30   $277.30  
  Purchase #2 $241.72   11.506%   $269.5323   $269.53   $269.55   $269.50  
  Purchase #3 $22.99   4.381%   $23.9972   $24.00   $24.00   $24.00  
  Purchase #4 $117.71   6.829%   $125.7484   $125.75   $125.75   $125.70  
  Purchase #5 $28.91   11.356%   $32.193   $32.19   $32.20   $32.20  
  Purchase #6 $59.97   8.298%   $64.9463   $64.95   $64.95   $64.90  
  Purchase #7 $245.69   5.738%   $259.7877   $259.79   $259.80   $259.80  
  7 purchase totals = $962.70       $1,053.4960   $1,053.50   $1,053.55   $1,053.40