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 $201.80   10.798%   $223.5904   $223.59   $223.60   $223.60  
  Purchase #2 $223.73   13.393%   $253.6942   $253.69   $253.70   $253.70  
  Purchase #3 $48.45   11.446%   $53.9956   $54.00   $54.00   $54.00  
  Purchase #4 $199.72   9.643%   $218.979   $218.98   $219.00   $219.00  
  Purchase #5 $92.99   7.802%   $100.2451   $100.25   $100.25   $100.20  
  Purchase #6 $221.32   6.534%   $235.781   $235.78   $235.80   $235.80  
  Purchase #7 $19.39   6.573%   $20.6645   $20.66   $20.65   $20.70  
  7 purchase totals = $1,007.40       $1,106.9498   $1,106.95   $1,107.00   $1,107.00