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 $124.28   10.657%   $137.5245   $137.52   $137.50   $137.50  
  Purchase #2 $57.72   12.319%   $64.8305   $64.83   $64.85   $64.80  
  Purchase #3 $202.75   10.818%   $224.6835   $224.68   $224.70   $224.70  
  Purchase #4 $212.33   6.134%   $225.3543   $225.35   $225.35   $225.40  
  Purchase #5 $77.76   6.857%   $83.092   $83.09   $83.10   $83.10  
  Purchase #6 $29.55   6.249%   $31.3966   $31.40   $31.40   $31.40  
  Purchase #7 $245.40   3.118%   $253.0516   $253.05   $253.05   $253.10  
  7 purchase totals = $949.79       $1,019.9330   $1,019.92   $1,019.95   $1,020.00