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 $245.39   6.663%   $261.7403   $261.74   $261.75   $261.70  
  Purchase #2 $141.65   11.436%   $157.8491   $157.85   $157.85   $157.80  
  Purchase #3 $12.32   12.162%   $13.8184   $13.82   $13.80   $13.80  
  Purchase #4 $151.94   6.438%   $161.7219   $161.72   $161.70   $161.70  
  Purchase #5 $193.50   5.236%   $203.6317   $203.63   $203.65   $203.60  
  Purchase #6 $80.57   6.521%   $85.824   $85.82   $85.80   $85.80  
  Purchase #7 $64.50   6.115%   $68.4442   $68.44   $68.45   $68.40  
  7 purchase totals = $889.87       $953.0296   $953.02   $953.00   $952.80