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 $152.41   10.359%   $168.1982   $168.20   $168.20   $168.20  
  Purchase #2 $56.73   3.597%   $58.7706   $58.77   $58.75   $58.80  
  Purchase #3 $138.35   7.147%   $148.2379   $148.24   $148.25   $148.20  
  Purchase #4 $216.98   3.457%   $224.481   $224.48   $224.50   $224.50  
  Purchase #5 $201.98   8.603%   $219.3563   $219.36   $219.35   $219.40  
  Purchase #6 $150.88   3.523%   $156.1955   $156.20   $156.20   $156.20  
  Purchase #7 $30.96   8.471%   $33.5826   $33.58   $33.60   $33.60  
  7 purchase totals = $948.29       $1,008.8221   $1,008.83   $1,008.85   $1,008.90