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 $78.26   9.233%   $85.4857   $85.49   $85.50   $85.50  
  Purchase #2 $120.95   13.120%   $136.8186   $136.82   $136.80   $136.80  
  Purchase #3 $67.36   10.815%   $74.645   $74.65   $74.65   $74.60  
  Purchase #4 $221.83   11.344%   $246.9944   $246.99   $247.00   $247.00  
  Purchase #5 $175.72   11.389%   $195.7328   $195.73   $195.75   $195.70  
  Purchase #6 $231.25   11.130%   $256.9881   $256.99   $257.00   $257.00  
  Purchase #7 $31.42   9.127%   $34.2877   $34.29   $34.30   $34.30  
  7 purchase totals = $926.79       $1,030.9523   $1,030.96   $1,031.00   $1,030.90