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 $107.72   4.813%   $112.9046   $112.90   $112.90   $112.90  
  Purchase #2 $105.33   7.354%   $113.076   $113.08   $113.10   $113.10  
  Purchase #3 $78.60   11.710%   $87.8041   $87.80   $87.80   $87.80  
  Purchase #4 $91.57   7.508%   $98.4451   $98.45   $98.45   $98.40  
  Purchase #5 $77.49   3.287%   $80.0371   $80.04   $80.05   $80.00  
  Purchase #6 $126.93   10.852%   $140.7044   $140.70   $140.70   $140.70  
  Purchase #7 $159.27   11.727%   $177.9476   $177.95   $177.95   $177.90  
  7 purchase totals = $746.91       $810.9189   $810.92   $810.95   $810.80