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 $224.61   12.801%   $253.3623   $253.36   $253.35   $253.40  
  Purchase #2 $177.85   9.114%   $194.0592   $194.06   $194.05   $194.10  
  Purchase #3 $149.76   5.399%   $157.8455   $157.85   $157.85   $157.80  
  Purchase #4 $118.94   3.842%   $123.5097   $123.51   $123.50   $123.50  
  Purchase #5 $91.83   3.694%   $95.2222   $95.22   $95.20   $95.20  
  Purchase #6 $31.54   11.700%   $35.2302   $35.23   $35.25   $35.20  
  Purchase #7 $187.73   3.843%   $194.9445   $194.94   $194.95   $194.90  
  7 purchase totals = $982.26       $1,054.1736   $1,054.17   $1,054.15   $1,054.10