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 $227.33   11.523%   $253.5252   $253.53   $253.55   $253.50  
  Purchase #2 $33.74   9.672%   $37.0033   $37.00   $37.00   $37.00  
  Purchase #3 $213.54   11.343%   $237.7618   $237.76   $237.75   $237.80  
  Purchase #4 $243.51   6.303%   $258.8584   $258.86   $258.85   $258.90  
  Purchase #5 $41.70   13.231%   $47.2173   $47.22   $47.20   $47.20  
  Purchase #6 $241.72   10.474%   $267.0378   $267.04   $267.05   $267.00  
  Purchase #7 $171.57   8.644%   $186.4005   $186.40   $186.40   $186.40  
  7 purchase totals = $1,173.11       $1,287.8043   $1,287.81   $1,287.80   $1,287.80