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 $53.37   6.171%   $56.6635   $56.66   $56.65   $56.70  
  Purchase #2 $231.31   9.129%   $252.4263   $252.43   $252.45   $252.40  
  Purchase #3 $117.52   4.676%   $123.0152   $123.02   $123.00   $123.00  
  Purchase #4 $93.84   9.706%   $102.9481   $102.95   $102.95   $102.90  
  Purchase #5 $200.82   3.161%   $207.1679   $207.17   $207.15   $207.20  
  Purchase #6 $232.95   5.722%   $246.2794   $246.28   $246.30   $246.30  
  Purchase #7 $73.63   7.677%   $79.2826   $79.28   $79.30   $79.30  
  7 purchase totals = $1,003.44       $1,067.7830   $1,067.79   $1,067.80   $1,067.80