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 $184.57   9.421%   $201.9583   $201.96   $201.95   $202.00  
  Purchase #2 $232.35   7.652%   $250.1294   $250.13   $250.15   $250.10  
  Purchase #3 $184.47   13.265%   $208.9399   $208.94   $208.95   $208.90  
  Purchase #4 $211.87   7.327%   $227.3937   $227.39   $227.40   $227.40  
  Purchase #5 $241.87   3.871%   $251.2328   $251.23   $251.25   $251.20  
  Purchase #6 $167.40   7.412%   $179.8077   $179.81   $179.80   $179.80  
  Purchase #7 $158.64   12.482%   $178.4414   $178.44   $178.45   $178.40  
  7 purchase totals = $1,381.17       $1,497.9032   $1,497.90   $1,497.95   $1,497.80