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 $228.61   3.153%   $235.8181   $235.82   $235.80   $235.80  
  Purchase #2 $191.77   5.254%   $201.8456   $201.85   $201.85   $201.80  
  Purchase #3 $197.46   8.810%   $214.8562   $214.86   $214.85   $214.90  
  Purchase #4 $100.68   6.234%   $106.9564   $106.96   $106.95   $107.00  
  Purchase #5 $93.96   3.401%   $97.1556   $97.16   $97.15   $97.20  
  Purchase #6 $30.54   12.739%   $34.4305   $34.43   $34.45   $34.40  
  Purchase #7 $83.54   3.475%   $86.443   $86.44   $86.45   $86.40  
  7 purchase totals = $926.56       $977.5054   $977.52   $977.50   $977.50