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 $134.92   13.444%   $153.0586   $153.06   $153.05   $153.10  
  Purchase #2 $141.95   13.232%   $160.7328   $160.73   $160.75   $160.70  
  Purchase #3 $179.28   8.185%   $193.9541   $193.95   $193.95   $194.00  
  Purchase #4 $73.81   13.443%   $83.7323   $83.73   $83.75   $83.70  
  Purchase #5 $185.56   11.410%   $206.7324   $206.73   $206.75   $206.70  
  Purchase #6 $120.34   3.577%   $124.6446   $124.64   $124.65   $124.60  
  Purchase #7 $135.27   12.849%   $152.6508   $152.65   $152.65   $152.70  
  7 purchase totals = $971.13       $1,075.5056   $1,075.49   $1,075.55   $1,075.50