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 $211.45   8.138%   $228.6578   $228.66   $228.65   $228.70  
  Purchase #2 $53.78   3.544%   $55.686   $55.69   $55.70   $55.70  
  Purchase #3 $23.27   13.235%   $26.3498   $26.35   $26.35   $26.30  
  Purchase #4 $190.83   3.670%   $197.8335   $197.83   $197.85   $197.80  
  Purchase #5 $232.92   8.335%   $252.3339   $252.33   $252.35   $252.30  
  Purchase #6 $243.37   9.485%   $266.4536   $266.45   $266.45   $266.50  
  Purchase #7 $30.88   8.415%   $33.4786   $33.48   $33.50   $33.50  
  7 purchase totals = $986.50       $1,060.7932   $1,060.79   $1,060.85   $1,060.80