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 $250.53   5.758%   $264.9555   $264.96   $264.95   $265.00  
  Purchase #2 $123.47   9.568%   $135.2836   $135.28   $135.30   $135.30  
  Purchase #3 $172.32   6.763%   $183.974   $183.97   $183.95   $184.00  
  Purchase #4 $168.54   12.441%   $189.5081   $189.51   $189.50   $189.50  
  Purchase #5 $228.57   7.197%   $245.0202   $245.02   $245.00   $245.00  
  Purchase #6 $147.59   6.212%   $156.7583   $156.76   $156.75   $156.80  
  Purchase #7 $90.30   7.358%   $96.9443   $96.94   $96.95   $96.90  
  7 purchase totals = $1,181.32       $1,272.4440   $1,272.44   $1,272.40   $1,272.50