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 $94.45   10.701%   $104.5571   $104.56   $104.55   $104.60  
  Purchase #2 $153.71   8.536%   $166.8307   $166.83   $166.85   $166.80  
  Purchase #3 $20.56   5.716%   $21.7352   $21.74   $21.75   $21.70  
  Purchase #4 $182.34   5.366%   $192.1244   $192.12   $192.10   $192.10  
  Purchase #5 $230.62   5.457%   $243.2049   $243.20   $243.20   $243.20  
  Purchase #6 $106.28   12.453%   $119.515   $119.52   $119.50   $119.50  
  Purchase #7 $124.33   8.433%   $134.8147   $134.81   $134.80   $134.80  
  7 purchase totals = $912.29       $982.7820   $982.78   $982.75   $982.70