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 $246.33   6.778%   $263.0262   $263.03   $263.05   $263.00  
  Purchase #2 $168.29   13.471%   $190.9603   $190.96   $190.95   $191.00  
  Purchase #3 $59.47   3.767%   $61.7102   $61.71   $61.70   $61.70  
  Purchase #4 $138.51   6.808%   $147.9398   $147.94   $147.95   $147.90  
  Purchase #5 $241.87   13.501%   $274.5249   $274.52   $274.50   $274.50  
  Purchase #6 $22.77   9.105%   $24.8432   $24.84   $24.85   $24.80  
  Purchase #7 $8.56   12.680%   $9.6454   $9.65   $9.65   $9.60  
  7 purchase totals = $885.80       $972.6500   $972.65   $972.65   $972.50