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 $205.51   6.543%   $218.9565   $218.96   $218.95   $219.00  
  Purchase #2 $165.60   8.266%   $179.2885   $179.29   $179.30   $179.30  
  Purchase #3 $247.57   6.489%   $263.6348   $263.63   $263.65   $263.60  
  Purchase #4 $42.62   9.424%   $46.6365   $46.64   $46.65   $46.60  
  Purchase #5 $12.74   13.715%   $14.4873   $14.49   $14.50   $14.50  
  Purchase #6 $38.72   9.781%   $42.5072   $42.51   $42.50   $42.50  
  Purchase #7 $169.70   7.597%   $182.5921   $182.59   $182.60   $182.60  
  7 purchase totals = $882.46       $948.1029   $948.11   $948.15   $948.10