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 $154.56   13.583%   $175.5539   $175.55   $175.55   $175.60  
  Purchase #2 $212.87   10.702%   $235.6513   $235.65   $235.65   $235.70  
  Purchase #3 $9.81   7.245%   $10.5207   $10.52   $10.50   $10.50  
  Purchase #4 $137.71   12.469%   $154.8811   $154.88   $154.90   $154.90  
  Purchase #5 $136.42   5.384%   $143.7649   $143.76   $143.75   $143.80  
  Purchase #6 $173.43   8.381%   $187.9652   $187.97   $187.95   $188.00  
  Purchase #7 $61.31   5.289%   $64.5527   $64.55   $64.55   $64.60  
  7 purchase totals = $886.11       $972.8898   $972.88   $972.85   $973.10