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 $126.87   11.540%   $141.5108   $141.51   $141.50   $141.50  
  Purchase #2 $189.81   12.569%   $213.6672   $213.67   $213.65   $213.70  
  Purchase #3 $119.69   10.590%   $132.3652   $132.37   $132.35   $132.40  
  Purchase #4 $69.96   13.427%   $79.3535   $79.35   $79.35   $79.40  
  Purchase #5 $178.64   12.174%   $200.3876   $200.39   $200.40   $200.40  
  Purchase #6 $29.95   10.350%   $33.0498   $33.05   $33.05   $33.00  
  Purchase #7 $220.97   5.285%   $232.6483   $232.65   $232.65   $232.60  
  7 purchase totals = $935.89       $1,032.9824   $1,032.99   $1,032.95   $1,033.00