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 $81.98   12.634%   $92.3374   $92.34   $92.35   $92.30  
  Purchase #2 $129.93   13.485%   $147.4511   $147.45   $147.45   $147.50  
  Purchase #3 $216.33   4.361%   $225.7642   $225.76   $225.75   $225.80  
  Purchase #4 $31.27   9.866%   $34.3551   $34.36   $34.35   $34.40  
  Purchase #5 $117.70   5.710%   $124.4207   $124.42   $124.40   $124.40  
  Purchase #6 $183.95   11.803%   $205.6616   $205.66   $205.65   $205.70  
  Purchase #7 $172.86   6.303%   $183.7554   $183.76   $183.75   $183.80  
  7 purchase totals = $934.02       $1,013.7455   $1,013.75   $1,013.70   $1,013.90