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 $12.98   12.158%   $14.5581   $14.56   $14.55   $14.60  
  Purchase #2 $142.89   6.550%   $152.2493   $152.25   $152.25   $152.20  
  Purchase #3 $234.37   5.223%   $246.6111   $246.61   $246.60   $246.60  
  Purchase #4 $169.45   13.770%   $192.7833   $192.78   $192.80   $192.80  
  Purchase #5 $179.93   9.726%   $197.43   $197.43   $197.45   $197.40  
  Purchase #6 $181.73   8.819%   $197.7568   $197.76   $197.75   $197.80  
  Purchase #7 $134.26   5.776%   $142.0149   $142.01   $142.00   $142.00  
  7 purchase totals = $1,055.61       $1,143.4035   $1,143.40   $1,143.40   $1,143.40