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 $160.51   12.473%   $180.5304   $180.53   $180.55   $180.50  
  Purchase #2 $169.35   10.784%   $187.6127   $187.61   $187.60   $187.60  
  Purchase #3 $12.61   10.711%   $13.9607   $13.96   $13.95   $14.00  
  Purchase #4 $84.90   12.104%   $95.1763   $95.18   $95.20   $95.20  
  Purchase #5 $23.90   11.294%   $26.5993   $26.60   $26.60   $26.60  
  Purchase #6 $206.92   13.809%   $235.4936   $235.49   $235.50   $235.50  
  Purchase #7 $229.70   7.163%   $246.1534   $246.15   $246.15   $246.20  
  7 purchase totals = $887.89       $985.5264   $985.52   $985.55   $985.60