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 $162.69   12.545%   $183.0995   $183.10   $183.10   $183.10  
  Purchase #2 $133.30   9.610%   $146.1101   $146.11   $146.10   $146.10  
  Purchase #3 $216.80   13.464%   $245.99   $245.99   $246.00   $246.00  
  Purchase #4 $67.92   5.710%   $71.7982   $71.80   $71.80   $71.80  
  Purchase #5 $86.30   11.860%   $96.5352   $96.54   $96.55   $96.50  
  Purchase #6 $48.45   6.368%   $51.5353   $51.54   $51.55   $51.50  
  Purchase #7 $245.52   11.647%   $274.1157   $274.12   $274.10   $274.10  
  7 purchase totals = $960.98       $1,069.1840   $1,069.20   $1,069.20   $1,069.10