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 $71.29   9.161%   $77.8209   $77.82   $77.80   $77.80  
  Purchase #2 $137.61   10.348%   $151.8499   $151.85   $151.85   $151.80  
  Purchase #3 $106.26   4.831%   $111.3934   $111.39   $111.40   $111.40  
  Purchase #4 $249.73   13.861%   $284.3451   $284.35   $284.35   $284.30  
  Purchase #5 $181.82   12.637%   $204.7966   $204.80   $204.80   $204.80  
  Purchase #6 $11.40   9.195%   $12.4482   $12.45   $12.45   $12.40  
  Purchase #7 $78.42   11.485%   $87.4265   $87.43   $87.45   $87.40  
  7 purchase totals = $836.53       $930.0806   $930.09   $930.10   $929.90