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 $94.79   3.388%   $98.0015   $98.00   $98.00   $98.00  
  Purchase #2 $55.46   6.730%   $59.1925   $59.19   $59.20   $59.20  
  Purchase #3 $79.98   3.128%   $82.4818   $82.48   $82.50   $82.50  
  Purchase #4 $193.25   4.486%   $201.9192   $201.92   $201.90   $201.90  
  Purchase #5 $5.43   9.242%   $5.9318   $5.93   $5.95   $5.90  
  Purchase #6 $140.94   9.279%   $154.0178   $154.02   $154.00   $154.00  
  Purchase #7 $162.54   11.852%   $181.8042   $181.80   $181.80   $181.80  
  7 purchase totals = $732.39       $783.3488   $783.34   $783.35   $783.30