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 $219.75   13.561%   $249.5503   $249.55   $249.55   $249.60  
  Purchase #2 $8.32   13.813%   $9.4692   $9.47   $9.45   $9.50  
  Purchase #3 $232.36   13.729%   $264.2607   $264.26   $264.25   $264.30  
  Purchase #4 $58.40   9.693%   $64.0607   $64.06   $64.05   $64.10  
  Purchase #5 $199.93   3.249%   $206.4257   $206.43   $206.45   $206.40  
  Purchase #6 $214.46   7.679%   $230.9284   $230.93   $230.95   $230.90  
  Purchase #7 $77.95   9.710%   $85.5189   $85.52   $85.50   $85.50  
  7 purchase totals = $1,011.17       $1,110.2139   $1,110.22   $1,110.20   $1,110.30