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 $96.74   4.752%   $101.3371   $101.34   $101.35   $101.30  
  Purchase #2 $249.60   13.638%   $283.6404   $283.64   $283.65   $283.60  
  Purchase #3 $52.53   11.351%   $58.4927   $58.49   $58.50   $58.50  
  Purchase #4 $179.38   5.611%   $189.445   $189.45   $189.45   $189.40  
  Purchase #5 $46.27   11.524%   $51.6022   $51.60   $51.60   $51.60  
  Purchase #6 $219.45   3.358%   $226.8191   $226.82   $226.80   $226.80  
  Purchase #7 $124.80   12.603%   $140.5285   $140.53   $140.55   $140.50  
  7 purchase totals = $968.77       $1,051.8650   $1,051.87   $1,051.90   $1,051.70