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 $94.86   12.540%   $106.7554   $106.76   $106.75   $106.80  
  Purchase #2 $218.80   7.183%   $234.5164   $234.52   $234.50   $234.50  
  Purchase #3 $78.36   9.855%   $86.0824   $86.08   $86.10   $86.10  
  Purchase #4 $241.81   9.547%   $264.8956   $264.90   $264.90   $264.90  
  Purchase #5 $186.62   4.484%   $194.988   $194.99   $195.00   $195.00  
  Purchase #6 $56.32   5.381%   $59.3506   $59.35   $59.35   $59.40  
  Purchase #7 $29.54   8.809%   $32.1422   $32.14   $32.15   $32.10  
  7 purchase totals = $906.31       $978.7306   $978.74   $978.75   $978.80