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 $95.61   7.420%   $102.7043   $102.70   $102.70   $102.70  
  Purchase #2 $153.87   10.522%   $170.0602   $170.06   $170.05   $170.10  
  Purchase #3 $95.60   4.811%   $100.1993   $100.20   $100.20   $100.20  
  Purchase #4 $78.98   5.344%   $83.2007   $83.20   $83.20   $83.20  
  Purchase #5 $181.25   7.493%   $194.8311   $194.83   $194.85   $194.80  
  Purchase #6 $175.48   9.665%   $192.4401   $192.44   $192.45   $192.40  
  Purchase #7 $206.96   10.358%   $228.3969   $228.40   $228.40   $228.40  
  7 purchase totals = $987.75       $1,071.8326   $1,071.83   $1,071.85   $1,071.80