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 $108.73   9.245%   $118.7821   $118.78   $118.80   $118.80  
  Purchase #2 $77.27   10.454%   $85.3478   $85.35   $85.35   $85.30  
  Purchase #3 $223.38   11.144%   $248.2735   $248.27   $248.25   $248.30  
  Purchase #4 $217.82   3.566%   $225.5875   $225.59   $225.60   $225.60  
  Purchase #5 $93.44   8.369%   $101.26   $101.26   $101.25   $101.30  
  Purchase #6 $212.78   9.208%   $232.3728   $232.37   $232.35   $232.40  
  Purchase #7 $62.52   3.295%   $64.58   $64.58   $64.60   $64.60  
  7 purchase totals = $995.94       $1,076.2037   $1,076.20   $1,076.20   $1,076.30