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 $80.85   13.287%   $91.5925   $91.59   $91.60   $91.60  
  Purchase #2 $189.98   11.424%   $211.6833   $211.68   $211.70   $211.70  
  Purchase #3 $237.44   11.515%   $264.7812   $264.78   $264.80   $264.80  
  Purchase #4 $193.55   5.498%   $204.1914   $204.19   $204.20   $204.20  
  Purchase #5 $91.49   3.436%   $94.6336   $94.63   $94.65   $94.60  
  Purchase #6 $231.28   3.509%   $239.3956   $239.40   $239.40   $239.40  
  Purchase #7 $164.32   7.469%   $176.5931   $176.59   $176.60   $176.60  
  7 purchase totals = $1,188.91       $1,282.8707   $1,282.86   $1,282.95   $1,282.90