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 $85.67   6.617%   $91.3388   $91.34   $91.35   $91.30  
  Purchase #2 $169.57   7.745%   $182.7032   $182.70   $182.70   $182.70  
  Purchase #3 $192.36   10.843%   $213.2176   $213.22   $213.20   $213.20  
  Purchase #4 $82.44   7.331%   $88.4837   $88.48   $88.50   $88.50  
  Purchase #5 $122.39   5.664%   $129.3222   $129.32   $129.30   $129.30  
  Purchase #6 $226.94   10.680%   $251.1772   $251.18   $251.20   $251.20  
  Purchase #7 $71.53   6.790%   $76.3869   $76.39   $76.40   $76.40  
  7 purchase totals = $950.90       $1,032.6296   $1,032.63   $1,032.65   $1,032.60