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 $236.85   5.699%   $250.3481   $250.35   $250.35   $250.30  
  Purchase #2 $22.54   4.787%   $23.619   $23.62   $23.60   $23.60  
  Purchase #3 $131.70   8.355%   $142.7035   $142.70   $142.70   $142.70  
  Purchase #4 $113.54   4.459%   $118.6027   $118.60   $118.60   $118.60  
  Purchase #5 $121.58   12.578%   $136.8723   $136.87   $136.85   $136.90  
  Purchase #6 $203.92   9.621%   $223.5391   $223.54   $223.55   $223.50  
  Purchase #7 $127.56   11.608%   $142.3672   $142.37   $142.35   $142.40  
  7 purchase totals = $957.69       $1,038.0519   $1,038.05   $1,038.00   $1,038.00