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 $61.44   10.692%   $68.0092   $68.01   $68.00   $68.00  
  Purchase #2 $127.31   11.214%   $141.5865   $141.59   $141.60   $141.60  
  Purchase #3 $105.35   6.144%   $111.8227   $111.82   $111.80   $111.80  
  Purchase #4 $238.37   12.125%   $267.2724   $267.27   $267.25   $267.30  
  Purchase #5 $177.74   9.337%   $194.3356   $194.34   $194.35   $194.30  
  Purchase #6 $5.88   10.613%   $6.504   $6.50   $6.50   $6.50  
  Purchase #7 $178.85   8.766%   $194.528   $194.53   $194.55   $194.50  
  7 purchase totals = $894.94       $984.0584   $984.06   $984.05   $984.00