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 $191.48   12.254%   $214.944   $214.94   $214.95   $214.90  
  Purchase #2 $175.26   12.331%   $196.8713   $196.87   $196.85   $196.90  
  Purchase #3 $56.87   5.704%   $60.1139   $60.11   $60.10   $60.10  
  Purchase #4 $125.82   3.422%   $130.1256   $130.13   $130.15   $130.10  
  Purchase #5 $208.80   4.534%   $218.267   $218.27   $218.25   $218.30  
  Purchase #6 $110.26   4.700%   $115.4422   $115.44   $115.45   $115.40  
  Purchase #7 $108.38   4.678%   $113.45   $113.45   $113.45   $113.50  
  7 purchase totals = $976.87       $1,049.2140   $1,049.21   $1,049.20   $1,049.20