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 $43.83   8.462%   $47.5389   $47.54   $47.55   $47.50  
  Purchase #2 $146.57   9.137%   $159.9621   $159.96   $159.95   $160.00  
  Purchase #3 $23.35   5.498%   $24.6338   $24.63   $24.65   $24.60  
  Purchase #4 $195.96   8.632%   $212.8753   $212.88   $212.90   $212.90  
  Purchase #5 $203.25   13.639%   $230.9713   $230.97   $230.95   $231.00  
  Purchase #6 $177.53   8.435%   $192.5047   $192.50   $192.50   $192.50  
  Purchase #7 $7.96   6.737%   $8.4963   $8.50   $8.50   $8.50  
  7 purchase totals = $798.45       $876.9824   $876.98   $877.00   $877.00