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 $134.36   12.599%   $151.288   $151.29   $151.30   $151.30  
  Purchase #2 $47.60   11.492%   $53.0702   $53.07   $53.05   $53.10  
  Purchase #3 $192.56   5.483%   $203.1181   $203.12   $203.10   $203.10  
  Purchase #4 $99.73   10.231%   $109.9334   $109.93   $109.95   $109.90  
  Purchase #5 $103.40   4.552%   $108.1068   $108.11   $108.10   $108.10  
  Purchase #6 $16.47   5.680%   $17.4055   $17.41   $17.40   $17.40  
  Purchase #7 $160.78   9.386%   $175.8708   $175.87   $175.85   $175.90  
  7 purchase totals = $754.90       $818.7928   $818.80   $818.75   $818.80