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 $57.38   9.751%   $62.9751   $62.98   $63.00   $63.00  
  Purchase #2 $237.78   3.415%   $245.9002   $245.90   $245.90   $245.90  
  Purchase #3 $36.65   5.474%   $38.6562   $38.66   $38.65   $38.70  
  Purchase #4 $112.88   4.523%   $117.9856   $117.99   $118.00   $118.00  
  Purchase #5 $129.34   9.459%   $141.5743   $141.57   $141.55   $141.60  
  Purchase #6 $159.29   9.411%   $174.2808   $174.28   $174.30   $174.30  
  Purchase #7 $220.70   12.872%   $249.1085   $249.11   $249.10   $249.10  
  7 purchase totals = $954.02       $1,030.4807   $1,030.49   $1,030.50   $1,030.60