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 $61.30   8.741%   $66.6582   $66.66   $66.65   $66.70  
  Purchase #2 $97.31   13.334%   $110.2853   $110.29   $110.30   $110.30  
  Purchase #3 $214.87   12.439%   $241.5977   $241.60   $241.60   $241.60  
  Purchase #4 $189.76   4.707%   $198.692   $198.69   $198.70   $198.70  
  Purchase #5 $41.54   12.464%   $46.7175   $46.72   $46.70   $46.70  
  Purchase #6 $197.45   11.399%   $219.9573   $219.96   $219.95   $220.00  
  Purchase #7 $70.96   7.120%   $76.0124   $76.01   $76.00   $76.00  
  7 purchase totals = $873.19       $959.9204   $959.93   $959.90   $960.00