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 $167.98   4.361%   $175.3056   $175.31   $175.30   $175.30  
  Purchase #2 $106.76   10.823%   $118.3146   $118.31   $118.30   $118.30  
  Purchase #3 $38.79   12.855%   $43.7765   $43.78   $43.80   $43.80  
  Purchase #4 $135.79   4.319%   $141.6548   $141.65   $141.65   $141.70  
  Purchase #5 $95.71   10.626%   $105.8801   $105.88   $105.90   $105.90  
  Purchase #6 $83.46   13.430%   $94.6687   $94.67   $94.65   $94.70  
  Purchase #7 $226.87   10.206%   $250.0244   $250.02   $250.00   $250.00  
  7 purchase totals = $855.36       $929.6247   $929.62   $929.60   $929.70