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 $227.74   7.864%   $245.6495   $245.65   $245.65   $245.60  
  Purchase #2 $30.37   8.625%   $32.9894   $32.99   $33.00   $33.00  
  Purchase #3 $246.61   12.138%   $276.5435   $276.54   $276.55   $276.50  
  Purchase #4 $21.87   11.697%   $24.4281   $24.43   $24.45   $24.40  
  Purchase #5 $40.28   10.346%   $44.4474   $44.45   $44.45   $44.40  
  Purchase #6 $228.61   7.590%   $245.9615   $245.96   $245.95   $246.00  
  Purchase #7 $172.45   5.267%   $181.5329   $181.53   $181.55   $181.50  
  7 purchase totals = $967.93       $1,051.5523   $1,051.55   $1,051.60   $1,051.40