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 $85.48   13.197%   $96.7608   $96.76   $96.75   $96.80  
  Purchase #2 $109.45   9.868%   $120.2505   $120.25   $120.25   $120.30  
  Purchase #3 $127.73   5.757%   $135.0834   $135.08   $135.10   $135.10  
  Purchase #4 $226.98   10.187%   $250.1025   $250.10   $250.10   $250.10  
  Purchase #5 $46.33   10.834%   $51.3494   $51.35   $51.35   $51.30  
  Purchase #6 $194.56   12.163%   $218.2243   $218.22   $218.20   $218.20  
  Purchase #7 $181.49   3.640%   $188.0962   $188.10   $188.10   $188.10  
  7 purchase totals = $972.02       $1,059.8671   $1,059.86   $1,059.85   $1,059.90