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 $91.65   3.561%   $94.9137   $94.91   $94.90   $94.90  
  Purchase #2 $119.81   13.524%   $136.0131   $136.01   $136.00   $136.00  
  Purchase #3 $111.34   3.867%   $115.6455   $115.65   $115.65   $115.60  
  Purchase #4 $57.55   9.438%   $62.9816   $62.98   $63.00   $63.00  
  Purchase #5 $93.64   5.748%   $99.0224   $99.02   $99.00   $99.00  
  Purchase #6 $8.85   7.707%   $9.5321   $9.53   $9.55   $9.50  
  Purchase #7 $159.36   9.217%   $174.0482   $174.05   $174.05   $174.00  
  7 purchase totals = $642.20       $692.1566   $692.15   $692.15   $692.00