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 $153.37   11.372%   $170.8112   $170.81   $170.80   $170.80  
  Purchase #2 $147.29   10.512%   $162.7731   $162.77   $162.75   $162.80  
  Purchase #3 $210.63   10.701%   $233.1695   $233.17   $233.15   $233.20  
  Purchase #4 $84.41   11.552%   $94.161   $94.16   $94.15   $94.20  
  Purchase #5 $32.58   4.868%   $34.166   $34.17   $34.15   $34.20  
  Purchase #6 $163.73   6.666%   $174.6442   $174.64   $174.65   $174.60  
  Purchase #7 $141.80   8.359%   $153.6531   $153.65   $153.65   $153.70  
  7 purchase totals = $933.81       $1,023.3781   $1,023.37   $1,023.30   $1,023.50