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 $90.75   8.852%   $98.7832   $98.78   $98.80   $98.80  
  Purchase #2 $155.74   12.139%   $174.6453   $174.65   $174.65   $174.60  
  Purchase #3 $241.98   6.415%   $257.503   $257.50   $257.50   $257.50  
  Purchase #4 $40.34   10.573%   $44.6051   $44.61   $44.60   $44.60  
  Purchase #5 $11.31   4.162%   $11.7807   $11.78   $11.80   $11.80  
  Purchase #6 $143.41   3.116%   $147.8787   $147.88   $147.90   $147.90  
  Purchase #7 $117.80   6.774%   $125.7798   $125.78   $125.80   $125.80  
  7 purchase totals = $801.33       $860.9758   $860.98   $861.05   $861.00