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 $206.25   12.409%   $231.8436   $231.84   $231.85   $231.80  
  Purchase #2 $98.36   8.763%   $106.9793   $106.98   $107.00   $107.00  
  Purchase #3 $147.77   11.253%   $164.3986   $164.40   $164.40   $164.40  
  Purchase #4 $246.31   3.729%   $255.4949   $255.49   $255.50   $255.50  
  Purchase #5 $119.87   13.141%   $135.6221   $135.62   $135.60   $135.60  
  Purchase #6 $133.96   10.655%   $148.2334   $148.23   $148.25   $148.20  
  Purchase #7 $72.53   12.767%   $81.7899   $81.79   $81.80   $81.80  
  7 purchase totals = $1,025.05       $1,124.3618   $1,124.35   $1,124.40   $1,124.30