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 $232.48   9.670%   $254.9608   $254.96   $254.95   $255.00  
  Purchase #2 $179.88   7.121%   $192.6893   $192.69   $192.70   $192.70  
  Purchase #3 $76.39   8.200%   $82.654   $82.65   $82.65   $82.70  
  Purchase #4 $80.85   13.462%   $91.734   $91.73   $91.75   $91.70  
  Purchase #5 $34.50   7.279%   $37.0113   $37.01   $37.00   $37.00  
  Purchase #6 $246.76   4.441%   $257.7186   $257.72   $257.70   $257.70  
  Purchase #7 $189.61   4.869%   $198.8421   $198.84   $198.85   $198.80  
  7 purchase totals = $1,040.47       $1,115.6101   $1,115.60   $1,115.60   $1,115.60