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 $29.64   13.296%   $33.5809   $33.58   $33.60   $33.60  
  Purchase #2 $225.92   9.601%   $247.6106   $247.61   $247.60   $247.60  
  Purchase #3 $22.36   11.402%   $24.9095   $24.91   $24.90   $24.90  
  Purchase #4 $148.76   6.749%   $158.7998   $158.80   $158.80   $158.80  
  Purchase #5 $58.34   9.732%   $64.0176   $64.02   $64.00   $64.00  
  Purchase #6 $195.64   3.198%   $201.8966   $201.90   $201.90   $201.90  
  Purchase #7 $110.25   5.574%   $116.3953   $116.40   $116.40   $116.40  
  7 purchase totals = $790.91       $847.2103   $847.22   $847.20   $847.20