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 $53.92   6.803%   $57.5882   $57.59   $57.60   $57.60  
  Purchase #2 $141.86   5.218%   $149.2623   $149.26   $149.25   $149.30  
  Purchase #3 $191.95   3.777%   $199.2   $199.20   $199.20   $199.20  
  Purchase #4 $95.46   4.582%   $99.834   $99.83   $99.85   $99.80  
  Purchase #5 $13.94   11.440%   $15.5347   $15.53   $15.55   $15.50  
  Purchase #6 $232.69   8.120%   $251.5844   $251.58   $251.60   $251.60  
  Purchase #7 $198.69   5.341%   $209.302   $209.30   $209.30   $209.30  
  7 purchase totals = $928.51       $982.3056   $982.29   $982.35   $982.30