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 $59.82   3.665%   $62.0124   $62.01   $62.00   $62.00  
  Purchase #2 $25.69   6.436%   $27.3434   $27.34   $27.35   $27.30  
  Purchase #3 $124.55   11.345%   $138.6802   $138.68   $138.70   $138.70  
  Purchase #4 $246.42   11.812%   $275.5271   $275.53   $275.55   $275.50  
  Purchase #5 $62.39   13.743%   $70.9643   $70.96   $70.95   $71.00  
  Purchase #6 $111.32   12.425%   $125.1515   $125.15   $125.15   $125.20  
  Purchase #7 $211.38   12.515%   $237.8342   $237.83   $237.85   $237.80  
  7 purchase totals = $841.57       $937.5131   $937.50   $937.55   $937.50