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 $201.81   10.811%   $223.6277   $223.63   $223.65   $223.60  
  Purchase #2 $64.44   4.393%   $67.2708   $67.27   $67.25   $67.30  
  Purchase #3 $158.26   7.499%   $170.1279   $170.13   $170.15   $170.10  
  Purchase #4 $36.57   12.680%   $41.2071   $41.21   $41.20   $41.20  
  Purchase #5 $247.83   9.285%   $270.841   $270.84   $270.85   $270.80  
  Purchase #6 $215.64   5.151%   $226.7476   $226.75   $226.75   $226.70  
  Purchase #7 $28.76   11.119%   $31.9578   $31.96   $31.95   $32.00  
  7 purchase totals = $953.31       $1,031.7799   $1,031.79   $1,031.80   $1,031.70