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 $59.46   10.779%   $65.8692   $65.87   $65.85   $65.90  
  Purchase #2 $63.75   5.485%   $67.2467   $67.25   $67.25   $67.20  
  Purchase #3 $112.87   6.256%   $119.9311   $119.93   $119.95   $119.90  
  Purchase #4 $51.29   11.797%   $57.3407   $57.34   $57.35   $57.30  
  Purchase #5 $212.62   8.631%   $230.9712   $230.97   $230.95   $231.00  
  Purchase #6 $36.69   3.211%   $37.8681   $37.87   $37.85   $37.90  
  Purchase #7 $195.92   13.194%   $221.7697   $221.77   $221.75   $221.80  
  7 purchase totals = $732.60       $800.9967   $801.00   $800.95   $801.00