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 $186.79   8.614%   $202.8801   $202.88   $202.90   $202.90  
  Purchase #2 $58.39   11.746%   $65.2485   $65.25   $65.25   $65.20  
  Purchase #3 $88.71   10.655%   $98.1621   $98.16   $98.15   $98.20  
  Purchase #4 $222.76   4.404%   $232.5704   $232.57   $232.55   $232.60  
  Purchase #5 $191.78   3.604%   $198.6918   $198.69   $198.70   $198.70  
  Purchase #6 $14.68   4.228%   $15.3007   $15.30   $15.30   $15.30  
  Purchase #7 $179.97   11.157%   $200.0493   $200.05   $200.05   $200.00  
  7 purchase totals = $943.08       $1,012.9029   $1,012.90   $1,012.90   $1,012.90