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 $194.52   11.184%   $216.2751   $216.28   $216.30   $216.30  
  Purchase #2 $137.82   12.649%   $155.2529   $155.25   $155.25   $155.30  
  Purchase #3 $165.84   4.643%   $173.54   $173.54   $173.55   $173.50  
  Purchase #4 $27.73   7.134%   $29.7083   $29.71   $29.70   $29.70  
  Purchase #5 $174.71   12.181%   $195.9914   $195.99   $196.00   $196.00  
  Purchase #6 $136.43   3.531%   $141.2473   $141.25   $141.25   $141.20  
  Purchase #7 $155.73   6.118%   $165.2576   $165.26   $165.25   $165.30  
  7 purchase totals = $992.78       $1,077.2726   $1,077.28   $1,077.30   $1,077.30