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 $122.76   9.590%   $134.5327   $134.53   $134.55   $134.50  
  Purchase #2 $174.96   4.758%   $183.2846   $183.28   $183.30   $183.30  
  Purchase #3 $14.43   6.600%   $15.3824   $15.38   $15.40   $15.40  
  Purchase #4 $146.51   3.743%   $151.9939   $151.99   $152.00   $152.00  
  Purchase #5 $217.60   12.443%   $244.676   $244.68   $244.70   $244.70  
  Purchase #6 $82.89   11.393%   $92.3337   $92.33   $92.35   $92.30  
  Purchase #7 $225.96   3.555%   $233.9929   $233.99   $234.00   $234.00  
  7 purchase totals = $985.11       $1,056.1962   $1,056.18   $1,056.30   $1,056.20