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 $118.71   5.797%   $125.5916   $125.59   $125.60   $125.60  
  Purchase #2 $70.86   12.797%   $79.928   $79.93   $79.95   $79.90  
  Purchase #3 $61.77   5.129%   $64.9382   $64.94   $64.95   $64.90  
  Purchase #4 $199.66   7.493%   $214.6205   $214.62   $214.60   $214.60  
  Purchase #5 $183.89   11.300%   $204.6696   $204.67   $204.65   $204.70  
  Purchase #6 $23.35   3.414%   $24.1472   $24.15   $24.15   $24.10  
  Purchase #7 $39.42   4.668%   $41.2601   $41.26   $41.25   $41.30  
  7 purchase totals = $697.66       $755.1552   $755.16   $755.15   $755.10