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 $184.29   6.745%   $196.7204   $196.72   $196.70   $196.70  
  Purchase #2 $92.86   3.636%   $96.2364   $96.24   $96.25   $96.20  
  Purchase #3 $235.63   4.738%   $246.7941   $246.79   $246.80   $246.80  
  Purchase #4 $151.55   4.250%   $157.9909   $157.99   $158.00   $158.00  
  Purchase #5 $135.53   8.785%   $147.4363   $147.44   $147.45   $147.40  
  Purchase #6 $81.84   13.421%   $92.8237   $92.82   $92.80   $92.80  
  Purchase #7 $108.34   6.439%   $115.316   $115.32   $115.30   $115.30  
  7 purchase totals = $990.04       $1,053.3178   $1,053.32   $1,053.30   $1,053.20