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 $221.87   11.658%   $247.7356   $247.74   $247.75   $247.70  
  Purchase #2 $160.85   8.381%   $174.3308   $174.33   $174.35   $174.30  
  Purchase #3 $155.40   10.369%   $171.5134   $171.51   $171.50   $171.50  
  Purchase #4 $196.67   9.306%   $214.9721   $214.97   $214.95   $215.00  
  Purchase #5 $236.61   6.641%   $252.3233   $252.32   $252.30   $252.30  
  Purchase #6 $161.74   10.857%   $179.3001   $179.30   $179.30   $179.30  
  Purchase #7 $57.68   9.511%   $63.1659   $63.17   $63.15   $63.20  
  7 purchase totals = $1,190.82       $1,303.3412   $1,303.34   $1,303.30   $1,303.30