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 $190.53   7.471%   $204.7645   $204.76   $204.75   $204.80  
  Purchase #2 $240.75   9.511%   $263.6477   $263.65   $263.65   $263.60  
  Purchase #3 $241.92   8.535%   $262.5679   $262.57   $262.55   $262.60  
  Purchase #4 $208.28   6.437%   $221.687   $221.69   $221.70   $221.70  
  Purchase #5 $49.40   8.650%   $53.6731   $53.67   $53.65   $53.70  
  Purchase #6 $196.44   3.847%   $203.997   $204.00   $204.00   $204.00  
  Purchase #7 $187.49   4.276%   $195.5071   $195.51   $195.50   $195.50  
  7 purchase totals = $1,314.81       $1,405.8443   $1,405.85   $1,405.80   $1,405.90