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 $228.87   12.600%   $257.7076   $257.71   $257.70   $257.70  
  Purchase #2 $71.51   13.250%   $80.9851   $80.99   $81.00   $81.00  
  Purchase #3 $173.65   13.810%   $197.6311   $197.63   $197.65   $197.60  
  Purchase #4 $234.41   13.850%   $266.8758   $266.88   $266.90   $266.90  
  Purchase #5 $16.93   11.187%   $18.824   $18.82   $18.80   $18.80  
  Purchase #6 $146.28   11.769%   $163.4957   $163.50   $163.50   $163.50  
  Purchase #7 $182.44   7.246%   $195.6596   $195.66   $195.65   $195.70  
  7 purchase totals = $1,054.09       $1,181.1789   $1,181.19   $1,181.20   $1,181.20