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 $179.31   8.493%   $194.5388   $194.54   $194.55   $194.50  
  Purchase #2 $31.84   4.613%   $33.3088   $33.31   $33.30   $33.30  
  Purchase #3 $186.45   11.162%   $207.2615   $207.26   $207.25   $207.30  
  Purchase #4 $29.47   13.310%   $33.3925   $33.39   $33.40   $33.40  
  Purchase #5 $184.70   11.861%   $206.6073   $206.61   $206.60   $206.60  
  Purchase #6 $244.62   4.707%   $256.1343   $256.13   $256.15   $256.10  
  Purchase #7 $127.42   5.130%   $133.9566   $133.96   $133.95   $134.00  
  7 purchase totals = $983.81       $1,065.1998   $1,065.20   $1,065.20   $1,065.20