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 $61.42   6.498%   $65.4111   $65.41   $65.40   $65.40  
  Purchase #2 $120.29   11.188%   $133.748   $133.75   $133.75   $133.70  
  Purchase #3 $247.29   8.680%   $268.7548   $268.75   $268.75   $268.80  
  Purchase #4 $20.97   4.440%   $21.9011   $21.90   $21.90   $21.90  
  Purchase #5 $246.81   8.846%   $268.6428   $268.64   $268.65   $268.60  
  Purchase #6 $231.98   5.192%   $244.0244   $244.02   $244.00   $244.00  
  Purchase #7 $119.30   9.591%   $130.7421   $130.74   $130.75   $130.70  
  7 purchase totals = $1,048.06       $1,133.2243   $1,133.21   $1,133.20   $1,133.10