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 $98.42   8.179%   $106.4698   $106.47   $106.45   $106.50  
  Purchase #2 $208.57   13.320%   $236.3515   $236.35   $236.35   $236.40  
  Purchase #3 $218.45   8.772%   $237.6124   $237.61   $237.60   $237.60  
  Purchase #4 $189.90   4.792%   $199   $199.00   $199.00   $199.00  
  Purchase #5 $17.33   9.498%   $18.976   $18.98   $19.00   $19.00  
  Purchase #6 $240.38   7.191%   $257.6657   $257.67   $257.65   $257.70  
  Purchase #7 $78.25   11.243%   $87.0476   $87.05   $87.05   $87.00  
  7 purchase totals = $1,051.30       $1,143.1230   $1,143.13   $1,143.10   $1,143.20