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 $131.82   7.448%   $141.638   $141.64   $141.65   $141.60  
  Purchase #2 $60.27   3.704%   $62.5024   $62.50   $62.50   $62.50  
  Purchase #3 $211.98   4.564%   $221.6548   $221.65   $221.65   $221.70  
  Purchase #4 $232.91   5.277%   $245.2007   $245.20   $245.20   $245.20  
  Purchase #5 $47.45   6.270%   $50.4251   $50.43   $50.45   $50.40  
  Purchase #6 $147.54   9.525%   $161.5932   $161.59   $161.60   $161.60  
  Purchase #7 $35.83   8.787%   $38.9784   $38.98   $39.00   $39.00  
  7 purchase totals = $867.80       $921.9926   $921.99   $922.05   $922.00