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 $208.34   13.264%   $235.9742   $235.97   $235.95   $236.00  
  Purchase #2 $122.71   7.222%   $131.5721   $131.57   $131.55   $131.60  
  Purchase #3 $152.75   11.741%   $170.6844   $170.68   $170.70   $170.70  
  Purchase #4 $246.69   9.730%   $270.6929   $270.69   $270.70   $270.70  
  Purchase #5 $58.71   3.604%   $60.8259   $60.83   $60.85   $60.80  
  Purchase #6 $163.62   6.425%   $174.1326   $174.13   $174.15   $174.10  
  Purchase #7 $176.86   12.443%   $198.8667   $198.87   $198.85   $198.90  
  7 purchase totals = $1,129.68       $1,242.7488   $1,242.74   $1,242.75   $1,242.80