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 $41.67   11.746%   $46.5646   $46.56   $46.55   $46.60  
  Purchase #2 $93.49   6.255%   $99.3378   $99.34   $99.35   $99.30  
  Purchase #3 $198.32   13.444%   $224.9821   $224.98   $225.00   $225.00  
  Purchase #4 $188.65   13.312%   $213.7631   $213.76   $213.75   $213.80  
  Purchase #5 $187.40   3.762%   $194.45   $194.45   $194.45   $194.50  
  Purchase #6 $158.96   5.450%   $167.6233   $167.62   $167.60   $167.60  
  Purchase #7 $227.76   8.827%   $247.8644   $247.86   $247.85   $247.90  
  7 purchase totals = $1,096.25       $1,194.5853   $1,194.57   $1,194.55   $1,194.70