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 $204.53   6.747%   $218.3296   $218.33   $218.35   $218.30  
  Purchase #2 $44.59   4.296%   $46.5056   $46.51   $46.50   $46.50  
  Purchase #3 $250.54   7.153%   $268.4611   $268.46   $268.45   $268.50  
  Purchase #4 $95.99   7.472%   $103.1624   $103.16   $103.15   $103.20  
  Purchase #5 $52.26   9.814%   $57.3888   $57.39   $57.40   $57.40  
  Purchase #6 $69.56   11.578%   $77.6137   $77.61   $77.60   $77.60  
  Purchase #7 $157.91   3.743%   $163.8206   $163.82   $163.80   $163.80  
  7 purchase totals = $875.38       $935.2818   $935.28   $935.25   $935.30