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 $194.99   6.159%   $206.9994   $207.00   $207.00   $207.00  
  Purchase #2 $56.26   3.336%   $58.1368   $58.14   $58.15   $58.10  
  Purchase #3 $54.47   10.211%   $60.0319   $60.03   $60.05   $60.00  
  Purchase #4 $51.82   12.856%   $58.482   $58.48   $58.50   $58.50  
  Purchase #5 $18.88   4.783%   $19.783   $19.78   $19.80   $19.80  
  Purchase #6 $182.27   6.745%   $194.5641   $194.56   $194.55   $194.60  
  Purchase #7 $71.96   5.374%   $75.8271   $75.83   $75.85   $75.80  
  7 purchase totals = $630.65       $673.8243   $673.82   $673.90   $673.80