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 $181.67   13.559%   $206.3026   $206.30   $206.30   $206.30  
  Purchase #2 $69.64   9.797%   $76.4626   $76.46   $76.45   $76.50  
  Purchase #3 $192.56   5.430%   $203.016   $203.02   $203.00   $203.00  
  Purchase #4 $26.72   3.354%   $27.6162   $27.62   $27.60   $27.60  
  Purchase #5 $56.96   9.430%   $62.3313   $62.33   $62.35   $62.30  
  Purchase #6 $167.88   9.827%   $184.3776   $184.38   $184.40   $184.40  
  Purchase #7 $57.87   9.640%   $63.4487   $63.45   $63.45   $63.40  
  7 purchase totals = $753.30       $823.5550   $823.56   $823.55   $823.50