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 $202.36   5.743%   $213.9815   $213.98   $214.00   $214.00  
  Purchase #2 $104.30   7.316%   $111.9306   $111.93   $111.95   $111.90  
  Purchase #3 $27.86   9.163%   $30.4128   $30.41   $30.40   $30.40  
  Purchase #4 $232.38   6.431%   $247.3244   $247.32   $247.30   $247.30  
  Purchase #5 $130.46   5.234%   $137.2883   $137.29   $137.30   $137.30  
  Purchase #6 $245.29   4.609%   $256.5954   $256.60   $256.60   $256.60  
  Purchase #7 $205.78   5.363%   $216.816   $216.82   $216.80   $216.80  
  7 purchase totals = $1,148.43       $1,214.3490   $1,214.35   $1,214.35   $1,214.30