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 $174.47   7.134%   $186.9167   $186.92   $186.90   $186.90  
  Purchase #2 $235.48   4.460%   $245.9824   $245.98   $246.00   $246.00  
  Purchase #3 $108.86   13.736%   $123.813   $123.81   $123.80   $123.80  
  Purchase #4 $145.46   8.296%   $157.5274   $157.53   $157.55   $157.50  
  Purchase #5 $123.27   5.316%   $129.823   $129.82   $129.80   $129.80  
  Purchase #6 $212.63   5.455%   $224.229   $224.23   $224.25   $224.20  
  Purchase #7 $131.58   5.302%   $138.5564   $138.56   $138.55   $138.60  
  7 purchase totals = $1,131.75       $1,206.8479   $1,206.85   $1,206.85   $1,206.80