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 $67.53   10.853%   $74.859   $74.86   $74.85   $74.90  
  Purchase #2 $184.42   11.525%   $205.6744   $205.67   $205.65   $205.70  
  Purchase #3 $119.93   13.380%   $135.9766   $135.98   $136.00   $136.00  
  Purchase #4 $246.65   5.110%   $259.2538   $259.25   $259.25   $259.30  
  Purchase #5 $118.65   9.725%   $130.1887   $130.19   $130.20   $130.20  
  Purchase #6 $58.94   5.472%   $62.1652   $62.17   $62.15   $62.20  
  Purchase #7 $40.36   4.677%   $42.2476   $42.25   $42.25   $42.20  
  7 purchase totals = $836.48       $910.3653   $910.37   $910.35   $910.50