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 $117.65   10.556%   $130.0691   $130.07   $130.05   $130.10  
  Purchase #2 $250.49   3.639%   $259.6053   $259.61   $259.60   $259.60  
  Purchase #3 $24.92   7.345%   $26.7504   $26.75   $26.75   $26.80  
  Purchase #4 $86.48   9.620%   $94.7994   $94.80   $94.80   $94.80  
  Purchase #5 $213.35   13.187%   $241.4845   $241.48   $241.50   $241.50  
  Purchase #6 $203.33   13.573%   $230.928   $230.93   $230.95   $230.90  
  Purchase #7 $230.52   7.280%   $247.3019   $247.30   $247.30   $247.30  
  7 purchase totals = $1,126.74       $1,230.9386   $1,230.94   $1,230.95   $1,231.00