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 $56.68   5.241%   $59.6506   $59.65   $59.65   $59.70  
  Purchase #2 $132.39   12.199%   $148.5403   $148.54   $148.55   $148.50  
  Purchase #3 $230.49   12.532%   $259.375   $259.38   $259.40   $259.40  
  Purchase #4 $158.53   8.662%   $172.2619   $172.26   $172.25   $172.30  
  Purchase #5 $32.60   10.764%   $36.1091   $36.11   $36.10   $36.10  
  Purchase #6 $83.60   12.354%   $93.9279   $93.93   $93.95   $93.90  
  Purchase #7 $107.56   7.569%   $115.7012   $115.70   $115.70   $115.70  
  7 purchase totals = $801.85       $885.5660   $885.57   $885.60   $885.60