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 $219.39   6.208%   $233.0097   $233.01   $233.00   $233.00  
  Purchase #2 $133.94   6.500%   $142.6461   $142.65   $142.65   $142.60  
  Purchase #3 $169.64   9.239%   $185.313   $185.31   $185.30   $185.30  
  Purchase #4 $208.90   7.199%   $223.9387   $223.94   $223.95   $223.90  
  Purchase #5 $56.74   11.444%   $63.2333   $63.23   $63.25   $63.20  
  Purchase #6 $230.69   3.397%   $238.5265   $238.53   $238.55   $238.50  
  Purchase #7 $207.95   3.306%   $214.8248   $214.82   $214.80   $214.80  
  7 purchase totals = $1,227.25       $1,301.4921   $1,301.49   $1,301.50   $1,301.30