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 $233.70   11.530%   $260.6456   $260.65   $260.65   $260.60  
  Purchase #2 $113.27   11.685%   $126.5056   $126.51   $126.50   $126.50  
  Purchase #3 $166.35   9.441%   $182.0551   $182.06   $182.05   $182.10  
  Purchase #4 $41.81   7.265%   $44.8475   $44.85   $44.85   $44.80  
  Purchase #5 $238.96   5.764%   $252.7337   $252.73   $252.75   $252.70  
  Purchase #6 $182.94   3.872%   $190.0234   $190.02   $190.00   $190.00  
  Purchase #7 $241.74   10.449%   $266.9994   $267.00   $267.00   $267.00  
  7 purchase totals = $1,218.77       $1,323.8103   $1,323.82   $1,323.80   $1,323.70