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 $88.98   5.211%   $93.6167   $93.62   $93.60   $93.60  
  Purchase #2 $226.51   5.852%   $239.7654   $239.77   $239.75   $239.80  
  Purchase #3 $233.81   9.374%   $255.7273   $255.73   $255.75   $255.70  
  Purchase #4 $162.54   11.425%   $181.1102   $181.11   $181.10   $181.10  
  Purchase #5 $56.71   9.623%   $62.1672   $62.17   $62.15   $62.20  
  Purchase #6 $31.95   13.600%   $36.2952   $36.30   $36.30   $36.30  
  Purchase #7 $117.49   8.692%   $127.7022   $127.70   $127.70   $127.70  
  7 purchase totals = $917.99       $996.3842   $996.40   $996.35   $996.40