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 $46.41   5.544%   $48.983   $48.98   $49.00   $49.00  
  Purchase #2 $115.30   4.281%   $120.236   $120.24   $120.25   $120.20  
  Purchase #3 $94.87   7.783%   $102.2537   $102.25   $102.25   $102.30  
  Purchase #4 $24.71   11.406%   $27.5284   $27.53   $27.55   $27.50  
  Purchase #5 $154.59   12.751%   $174.3018   $174.30   $174.30   $174.30  
  Purchase #6 $157.86   11.184%   $175.5151   $175.52   $175.50   $175.50  
  Purchase #7 $132.67   11.516%   $147.9483   $147.95   $147.95   $147.90  
  7 purchase totals = $726.41       $796.7663   $796.77   $796.80   $796.70