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 $54.34   13.262%   $61.5466   $61.55   $61.55   $61.50  
  Purchase #2 $154.91   4.789%   $162.3286   $162.33   $162.35   $162.30  
  Purchase #3 $136.84   3.544%   $141.6896   $141.69   $141.70   $141.70  
  Purchase #4 $25.33   5.608%   $26.7505   $26.75   $26.75   $26.80  
  Purchase #5 $217.98   10.315%   $240.4646   $240.46   $240.45   $240.50  
  Purchase #6 $150.77   11.117%   $167.5311   $167.53   $167.55   $167.50  
  Purchase #7 $22.43   4.734%   $23.4918   $23.49   $23.50   $23.50  
  7 purchase totals = $762.60       $823.8028   $823.80   $823.85   $823.80