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 $57.41   10.558%   $63.4713   $63.47   $63.45   $63.50  
  Purchase #2 $200.28   5.663%   $211.6219   $211.62   $211.60   $211.60  
  Purchase #3 $192.39   7.334%   $206.4999   $206.50   $206.50   $206.50  
  Purchase #4 $177.37   12.522%   $199.5803   $199.58   $199.60   $199.60  
  Purchase #5 $243.28   7.700%   $262.0126   $262.01   $262.00   $262.00  
  Purchase #6 $119.49   6.174%   $126.8673   $126.87   $126.85   $126.90  
  Purchase #7 $41.33   10.687%   $45.7469   $45.75   $45.75   $45.70  
  7 purchase totals = $1,031.55       $1,115.8002   $1,115.80   $1,115.75   $1,115.80