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 $51.55   11.380%   $57.4164   $57.42   $57.40   $57.40  
  Purchase #2 $116.90   12.658%   $131.6972   $131.70   $131.70   $131.70  
  Purchase #3 $234.59   6.855%   $250.6711   $250.67   $250.65   $250.70  
  Purchase #4 $110.82   4.519%   $115.828   $115.83   $115.85   $115.80  
  Purchase #5 $167.47   8.431%   $181.5894   $181.59   $181.60   $181.60  
  Purchase #6 $152.62   6.144%   $161.997   $162.00   $162.00   $162.00  
  Purchase #7 $146.57   8.195%   $158.5814   $158.58   $158.60   $158.60  
  7 purchase totals = $980.52       $1,057.7805   $1,057.79   $1,057.80   $1,057.80