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 $68.68   7.791%   $74.0309   $74.03   $74.05   $74.00  
  Purchase #2 $243.88   11.734%   $272.4969   $272.50   $272.50   $272.50  
  Purchase #3 $54.73   11.657%   $61.1099   $61.11   $61.10   $61.10  
  Purchase #4 $80.76   12.564%   $90.9067   $90.91   $90.90   $90.90  
  Purchase #5 $68.46   9.236%   $74.783   $74.78   $74.80   $74.80  
  Purchase #6 $159.38   10.380%   $175.9236   $175.92   $175.90   $175.90  
  Purchase #7 $110.98   11.703%   $123.968   $123.97   $123.95   $124.00  
  7 purchase totals = $786.87       $873.2190   $873.22   $873.20   $873.20