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 $235.40   13.501%   $267.1814   $267.18   $267.20   $267.20  
  Purchase #2 $58.64   4.679%   $61.3838   $61.38   $61.40   $61.40  
  Purchase #3 $22.51   13.512%   $25.5516   $25.55   $25.55   $25.60  
  Purchase #4 $156.33   7.486%   $168.0329   $168.03   $168.05   $168.00  
  Purchase #5 $218.64   11.835%   $244.516   $244.52   $244.50   $244.50  
  Purchase #6 $93.50   6.605%   $99.6757   $99.68   $99.70   $99.70  
  Purchase #7 $235.56   3.602%   $244.0449   $244.04   $244.05   $244.00  
  7 purchase totals = $1,020.58       $1,110.3863   $1,110.38   $1,110.45   $1,110.40