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 $238.50   3.128%   $245.9603   $245.96   $245.95   $246.00  
  Purchase #2 $198.65   6.578%   $211.7172   $211.72   $211.70   $211.70  
  Purchase #3 $145.64   6.736%   $155.4503   $155.45   $155.45   $155.50  
  Purchase #4 $235.88   4.558%   $246.6314   $246.63   $246.65   $246.60  
  Purchase #5 $93.46   9.797%   $102.6163   $102.62   $102.60   $102.60  
  Purchase #6 $206.98   3.858%   $214.9653   $214.97   $214.95   $215.00  
  Purchase #7 $49.84   13.723%   $56.6795   $56.68   $56.70   $56.70  
  7 purchase totals = $1,168.95       $1,234.0203   $1,234.03   $1,234.00   $1,234.10