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 $226.88   6.576%   $241.7996   $241.80   $241.80   $241.80  
  Purchase #2 $193.97   4.119%   $201.9596   $201.96   $201.95   $202.00  
  Purchase #3 $150.66   9.122%   $164.4032   $164.40   $164.40   $164.40  
  Purchase #4 $240.75   7.658%   $259.1866   $259.19   $259.20   $259.20  
  Purchase #5 $20.99   12.769%   $23.6702   $23.67   $23.65   $23.70  
  Purchase #6 $135.71   4.411%   $141.6962   $141.70   $141.70   $141.70  
  Purchase #7 $94.81   6.489%   $100.9622   $100.96   $100.95   $101.00  
  7 purchase totals = $1,063.77       $1,133.6776   $1,133.68   $1,133.65   $1,133.80