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 $244.32   5.195%   $257.0124   $257.01   $257.00   $257.00  
  Purchase #2 $243.52   9.431%   $266.4864   $266.49   $266.50   $266.50  
  Purchase #3 $250.44   5.481%   $264.1666   $264.17   $264.15   $264.20  
  Purchase #4 $96.42   10.335%   $106.385   $106.39   $106.40   $106.40  
  Purchase #5 $20.41   3.620%   $21.1488   $21.15   $21.15   $21.10  
  Purchase #6 $198.71   6.816%   $212.2541   $212.25   $212.25   $212.30  
  Purchase #7 $140.59   6.329%   $149.4879   $149.49   $149.50   $149.50  
  7 purchase totals = $1,194.41       $1,276.9412   $1,276.95   $1,276.95   $1,277.00