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 $119.67   11.710%   $133.6834   $133.68   $133.70   $133.70  
  Purchase #2 $200.35   9.192%   $218.7662   $218.77   $218.75   $218.80  
  Purchase #3 $210.44   12.582%   $236.9176   $236.92   $236.90   $236.90  
  Purchase #4 $95.68   8.183%   $103.5095   $103.51   $103.50   $103.50  
  Purchase #5 $176.27   12.423%   $198.168   $198.17   $198.15   $198.20  
  Purchase #6 $213.98   4.388%   $223.3694   $223.37   $223.35   $223.40  
  Purchase #7 $40.94   11.718%   $45.7373   $45.74   $45.75   $45.70  
  7 purchase totals = $1,057.33       $1,160.1514   $1,160.16   $1,160.10   $1,160.20