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 $61.69   3.717%   $63.983   $63.98   $64.00   $64.00  
  Purchase #2 $102.92   13.568%   $116.8842   $116.88   $116.90   $116.90  
  Purchase #3 $211.70   10.489%   $233.9052   $233.91   $233.90   $233.90  
  Purchase #4 $203.69   11.736%   $227.5951   $227.60   $227.60   $227.60  
  Purchase #5 $110.89   10.698%   $122.753   $122.75   $122.75   $122.80  
  Purchase #6 $200.70   12.726%   $226.2411   $226.24   $226.25   $226.20  
  Purchase #7 $101.85   3.209%   $105.1184   $105.12   $105.10   $105.10  
  7 purchase totals = $993.44       $1,096.4800   $1,096.48   $1,096.50   $1,096.50