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 $52.37   13.189%   $59.2771   $59.28   $59.30   $59.30  
  Purchase #2 $232.48   8.578%   $252.4221   $252.42   $252.40   $252.40  
  Purchase #3 $201.47   13.395%   $228.4569   $228.46   $228.45   $228.50  
  Purchase #4 $61.59   7.347%   $66.115   $66.12   $66.10   $66.10  
  Purchase #5 $66.77   10.604%   $73.8503   $73.85   $73.85   $73.90  
  Purchase #6 $189.88   6.378%   $201.9905   $201.99   $202.00   $202.00  
  Purchase #7 $232.59   10.222%   $256.3653   $256.37   $256.35   $256.40  
  7 purchase totals = $1,037.15       $1,138.4772   $1,138.49   $1,138.45   $1,138.60