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 $225.87   4.408%   $235.8263   $235.83   $235.85   $235.80  
  Purchase #2 $72.43   5.474%   $76.3948   $76.39   $76.40   $76.40  
  Purchase #3 $145.88   5.646%   $154.1164   $154.12   $154.10   $154.10  
  Purchase #4 $179.67   5.386%   $189.347   $189.35   $189.35   $189.30  
  Purchase #5 $87.25   8.156%   $94.3661   $94.37   $94.35   $94.40  
  Purchase #6 $86.36   9.450%   $94.521   $94.52   $94.50   $94.50  
  Purchase #7 $24.57   10.721%   $27.2041   $27.20   $27.20   $27.20  
  7 purchase totals = $822.03       $871.7757   $871.78   $871.75   $871.70