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 $216.43   11.401%   $241.1052   $241.11   $241.10   $241.10  
  Purchase #2 $61.64   3.242%   $63.6384   $63.64   $63.65   $63.60  
  Purchase #3 $134.49   7.722%   $144.8753   $144.88   $144.90   $144.90  
  Purchase #4 $204.32   4.544%   $213.6043   $213.60   $213.60   $213.60  
  Purchase #5 $48.56   4.328%   $50.6617   $50.66   $50.65   $50.70  
  Purchase #6 $141.37   12.625%   $159.218   $159.22   $159.20   $159.20  
  Purchase #7 $201.71   10.606%   $223.1034   $223.10   $223.10   $223.10  
  7 purchase totals = $1,008.52       $1,096.2063   $1,096.21   $1,096.20   $1,096.20