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 $85.56   8.160%   $92.5417   $92.54   $92.55   $92.50  
  Purchase #2 $39.75   9.813%   $43.6507   $43.65   $43.65   $43.70  
  Purchase #3 $223.49   10.193%   $246.2703   $246.27   $246.25   $246.30  
  Purchase #4 $233.35   4.870%   $244.7141   $244.71   $244.70   $244.70  
  Purchase #5 $222.42   4.664%   $232.7937   $232.79   $232.80   $232.80  
  Purchase #6 $19.88   6.428%   $21.1579   $21.16   $21.15   $21.20  
  Purchase #7 $131.29   10.678%   $145.3091   $145.31   $145.30   $145.30  
  7 purchase totals = $955.74       $1,026.4375   $1,026.43   $1,026.40   $1,026.50