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 $34.76   6.559%   $37.0399   $37.04   $37.05   $37.00  
  Purchase #2 $218.58   4.835%   $229.1483   $229.15   $229.15   $229.10  
  Purchase #3 $50.53   6.454%   $53.7912   $53.79   $53.80   $53.80  
  Purchase #4 $48.85   5.473%   $51.5236   $51.52   $51.50   $51.50  
  Purchase #5 $234.52   3.859%   $243.5701   $243.57   $243.55   $243.60  
  Purchase #6 $104.31   8.405%   $113.0773   $113.08   $113.10   $113.10  
  Purchase #7 $210.28   5.489%   $221.8223   $221.82   $221.80   $221.80  
  7 purchase totals = $901.83       $949.9727   $949.97   $949.95   $949.90