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 $84.97   10.391%   $93.7992   $93.80   $93.80   $93.80  
  Purchase #2 $112.41   8.679%   $122.1661   $122.17   $122.15   $122.20  
  Purchase #3 $232.87   9.491%   $254.9717   $254.97   $254.95   $255.00  
  Purchase #4 $96.40   8.522%   $104.6152   $104.62   $104.60   $104.60  
  Purchase #5 $53.76   4.174%   $56.0039   $56.00   $56.00   $56.00  
  Purchase #6 $222.95   4.800%   $233.6516   $233.65   $233.65   $233.70  
  Purchase #7 $213.70   6.809%   $228.2508   $228.25   $228.25   $228.30  
  7 purchase totals = $1,017.06       $1,093.4585   $1,093.46   $1,093.40   $1,093.60