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 $217.94   6.562%   $232.2412   $232.24   $232.25   $232.20  
  Purchase #2 $134.75   6.362%   $143.3228   $143.32   $143.30   $143.30  
  Purchase #3 $39.37   9.873%   $43.257   $43.26   $43.25   $43.30  
  Purchase #4 $145.73   5.432%   $153.6461   $153.65   $153.65   $153.60  
  Purchase #5 $65.46   6.147%   $69.4838   $69.48   $69.50   $69.50  
  Purchase #6 $233.46   9.467%   $255.5617   $255.56   $255.55   $255.60  
  Purchase #7 $71.88   8.786%   $78.1954   $78.20   $78.20   $78.20  
  7 purchase totals = $908.59       $975.7080   $975.71   $975.70   $975.70