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 $239.48   5.496%   $252.6418   $252.64   $252.65   $252.60  
  Purchase #2 $71.83   4.452%   $75.0279   $75.03   $75.05   $75.00  
  Purchase #3 $149.33   13.640%   $169.6986   $169.70   $169.70   $169.70  
  Purchase #4 $209.64   7.740%   $225.8661   $225.87   $225.85   $225.90  
  Purchase #5 $26.75   11.863%   $29.9234   $29.92   $29.90   $29.90  
  Purchase #6 $174.35   7.704%   $187.7819   $187.78   $187.80   $187.80  
  Purchase #7 $136.95   11.756%   $153.0498   $153.05   $153.05   $153.00  
  7 purchase totals = $1,008.33       $1,093.9895   $1,093.99   $1,094.00   $1,093.90