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 $34.46   6.231%   $36.6072   $36.61   $36.60   $36.60  
  Purchase #2 $54.33   9.686%   $59.5924   $59.59   $59.60   $59.60  
  Purchase #3 $35.49   4.606%   $37.1247   $37.12   $37.10   $37.10  
  Purchase #4 $163.45   12.613%   $184.0659   $184.07   $184.05   $184.10  
  Purchase #5 $237.79   3.448%   $245.989   $245.99   $246.00   $246.00  
  Purchase #6 $195.44   7.831%   $210.7449   $210.74   $210.75   $210.70  
  Purchase #7 $7.43   12.715%   $8.3747   $8.37   $8.35   $8.40  
  7 purchase totals = $728.39       $782.4988   $782.49   $782.45   $782.50