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 $187.61   8.661%   $203.8589   $203.86   $203.85   $203.90  
  Purchase #2 $246.56   3.511%   $255.2167   $255.22   $255.20   $255.20  
  Purchase #3 $248.83   8.803%   $270.7345   $270.73   $270.75   $270.70  
  Purchase #4 $162.51   5.645%   $171.6837   $171.68   $171.70   $171.70  
  Purchase #5 $175.41   4.433%   $183.1859   $183.19   $183.20   $183.20  
  Purchase #6 $112.78   4.336%   $117.6701   $117.67   $117.65   $117.70  
  Purchase #7 $39.69   11.394%   $44.2123   $44.21   $44.20   $44.20  
  7 purchase totals = $1,173.39       $1,246.5621   $1,246.56   $1,246.55   $1,246.60