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 $208.25   12.268%   $233.7981   $233.80   $233.80   $233.80  
  Purchase #2 $228.77   6.760%   $244.2349   $244.23   $244.25   $244.20  
  Purchase #3 $131.28   13.844%   $149.4544   $149.45   $149.45   $149.50  
  Purchase #4 $25.72   6.748%   $27.4556   $27.46   $27.45   $27.50  
  Purchase #5 $6.34   6.569%   $6.7565   $6.76   $6.75   $6.80  
  Purchase #6 $233.53   5.753%   $246.965   $246.97   $246.95   $247.00  
  Purchase #7 $152.37   7.373%   $163.6042   $163.60   $163.60   $163.60  
  7 purchase totals = $986.26       $1,072.2687   $1,072.27   $1,072.25   $1,072.40