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 $166.67   5.264%   $175.4435   $175.44   $175.45   $175.40  
  Purchase #2 $60.82   8.259%   $65.8431   $65.84   $65.85   $65.80  
  Purchase #3 $16.28   7.593%   $17.5161   $17.52   $17.50   $17.50  
  Purchase #4 $199.86   3.523%   $206.9011   $206.90   $206.90   $206.90  
  Purchase #5 $229.90   9.539%   $251.8302   $251.83   $251.85   $251.80  
  Purchase #6 $83.70   12.533%   $94.1901   $94.19   $94.20   $94.20  
  Purchase #7 $108.81   9.285%   $118.913   $118.91   $118.90   $118.90  
  7 purchase totals = $866.04       $930.6371   $930.63   $930.65   $930.50