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 $52.26   11.615%   $58.33   $58.33   $58.35   $58.30  
  Purchase #2 $56.88   5.374%   $59.9367   $59.94   $59.95   $59.90  
  Purchase #3 $235.44   9.569%   $257.9693   $257.97   $257.95   $258.00  
  Purchase #4 $197.98   4.569%   $207.0257   $207.03   $207.05   $207.00  
  Purchase #5 $250.89   6.324%   $266.7563   $266.76   $266.75   $266.80  
  Purchase #6 $134.83   4.739%   $141.2196   $141.22   $141.20   $141.20  
  Purchase #7 $174.67   5.228%   $183.8017   $183.80   $183.80   $183.80  
  7 purchase totals = $1,102.95       $1,175.0393   $1,175.05   $1,175.05   $1,175.00