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 $246.35   12.435%   $276.9836   $276.98   $277.00   $277.00  
  Purchase #2 $140.38   8.135%   $151.7999   $151.80   $151.80   $151.80  
  Purchase #3 $168.33   4.800%   $176.4098   $176.41   $176.40   $176.40  
  Purchase #4 $24.78   3.864%   $25.7375   $25.74   $25.75   $25.70  
  Purchase #5 $216.26   11.471%   $241.0672   $241.07   $241.05   $241.10  
  Purchase #6 $117.61   9.286%   $128.5313   $128.53   $128.55   $128.50  
  Purchase #7 $69.91   6.537%   $74.48   $74.48   $74.50   $74.50  
  7 purchase totals = $983.62       $1,075.0093   $1,075.01   $1,075.05   $1,075.00