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 $170.51   4.503%   $178.1881   $178.19   $178.20   $178.20  
  Purchase #2 $162.82   8.127%   $176.0524   $176.05   $176.05   $176.10  
  Purchase #3 $187.60   4.580%   $196.1921   $196.19   $196.20   $196.20  
  Purchase #4 $35.62   3.846%   $36.9899   $36.99   $37.00   $37.00  
  Purchase #5 $141.85   12.472%   $159.5415   $159.54   $159.55   $159.50  
  Purchase #6 $133.50   9.426%   $146.0837   $146.08   $146.10   $146.10  
  Purchase #7 $187.93   10.588%   $207.828   $207.83   $207.85   $207.80  
  7 purchase totals = $1,019.83       $1,100.8757   $1,100.87   $1,100.95   $1,100.90