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 $248.57   8.268%   $269.1218   $269.12   $269.10   $269.10  
  Purchase #2 $5.82   4.639%   $6.09   $6.09   $6.10   $6.10  
  Purchase #3 $196.88   3.359%   $203.4932   $203.49   $203.50   $203.50  
  Purchase #4 $53.60   13.847%   $61.022   $61.02   $61.00   $61.00  
  Purchase #5 $237.95   3.610%   $246.54   $246.54   $246.55   $246.50  
  Purchase #6 $180.84   10.625%   $200.0543   $200.05   $200.05   $200.10  
  Purchase #7 $211.40   6.860%   $225.902   $225.90   $225.90   $225.90  
  7 purchase totals = $1,135.06       $1,212.2233   $1,212.21   $1,212.20   $1,212.20