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 $216.87   7.361%   $232.8338   $232.83   $232.85   $232.80  
  Purchase #2 $249.57   13.355%   $282.9001   $282.90   $282.90   $282.90  
  Purchase #3 $16.81   3.149%   $17.3393   $17.34   $17.35   $17.30  
  Purchase #4 $197.35   3.173%   $203.6119   $203.61   $203.60   $203.60  
  Purchase #5 $219.58   3.258%   $226.7339   $226.73   $226.75   $226.70  
  Purchase #6 $222.54   12.141%   $249.5586   $249.56   $249.55   $249.60  
  Purchase #7 $56.70   4.344%   $59.163   $59.16   $59.15   $59.20  
  7 purchase totals = $1,179.42       $1,272.1406   $1,272.13   $1,272.15   $1,272.10