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 $218.90   11.782%   $244.6908   $244.69   $244.70   $244.70  
  Purchase #2 $179.46   4.342%   $187.2522   $187.25   $187.25   $187.30  
  Purchase #3 $27.43   8.502%   $29.7621   $29.76   $29.75   $29.80  
  Purchase #4 $69.40   5.691%   $73.3496   $73.35   $73.35   $73.30  
  Purchase #5 $144.30   5.537%   $152.2899   $152.29   $152.30   $152.30  
  Purchase #6 $65.31   4.133%   $68.0093   $68.01   $68.00   $68.00  
  Purchase #7 $226.90   4.580%   $237.292   $237.29   $237.30   $237.30  
  7 purchase totals = $931.70       $992.6459   $992.64   $992.65   $992.70